So, I've finally found MY headphones I tried the Sennheiser Momentum, the KEF M500, B&W P7, Sony MDR 1R, Philips Fidelio L2 (yes, the L2), the B&O H6, the Focal Spirit Classic (you read that right too) and the Sony MDR Z1000.
 
I was in search of a good sounding, but most of all comfortable closed headphone. All the headphones I've tried above sounded quite good, but none of them were comfortable enough for me (except for the Z1000, which is the 7520's less refined brother) so I ended up returning all of them.
 
So what was the first thing I noticed when I listened to the 7520? The amazing clarity. I'm not exaggerating when I say that all the above headphones (with the exception of maybe the L2) sound veiled compared to the 7520. Also the level of detail these headphones retrieve is amazing. It's actually leaning towards the analytical side, without losing it's musicality. I can listen to music for hours without the level of detail becoming too much, but when I want to close my eyes and focus on the music there is just oodles of detail to be found, I just get lost in the music
 
To my ears this headphone responds very well throughout the entire frequency range. The highs are nice and crisp but never sound harsh. Sometimes you will hear a bit of sibilance though, but that's only with less well mastered recordings. The mids are very neutral and detailed. And the bass is very very nicely done, very taught, controlled, and again I think fairly neutral. And it will still reach deep into sub-bass regions when the music calls for it. If a song is warm, the headphone will sound warm. If a song is cold, it'll sound cold. If the music is rocking, these headphones will rock. If the music is serene and quiet, these headphones will be very composed.
 
The soundstage of these headphones is also quite good. I'd say it portrays the soundstage the way the audio engineer intended it to sound (provided he was using good speakers/headphones as well of course ). So with classical music the soundstage can sound quite wide, and with other music it can sound quite narrow, depending on how it's recorded. I also feel like the imaging is done very well and the instrumental separation is excellent. When you focus you can and will hear every individual instrument, easily. And if you don't want to focus, it turns into a nice ensemble so you can just do what music is intended for: enjoyment
 
The Z1000 is the 7520's brother. They look exactly the same, just that the Z1000 has silver accents. I think they also use the same drivers as the technical specs are exactly the same, but others have pointed out that they are actually different drivers with very similar specs. Whatever the case is, they certainly do not sound the same. The bass response is a bit rolled off I'd say on the Z1000. It's just not there, even when the music calls for it. And compared to the 7520 the soundstaging was less expansive when the music called for it. The rest of the frequency range sounded otherwise fairly similar.
 
These headphones put a smile on my face when I listen to music. Eventhough they are marketed to the professional audio engineer market (and I can certainly hear why), I think any audiophile will be able to appreciate these headphones. I've never heard a truly neutral high-end headphone, so I cannot compare it to that, but I think this is quite close to a neutral sounding headphone.
 
I highly recommend this headphone to you all. At least give it a listen
 
Edit 3/25/2014: I lowered the rating by half a star as there is a bit of creaking in the headphone that I haven't been able to fix. It occurs when I move my head or jaw. It can be quite annoying. The SQ is still superb, but the creaking sometimes distracts me from my listening.

I've been looking for a decent pair of headphones that sound great, but also look nice enough that I'd be willing to be seen in public with them. And importantly, I want them to be comfortable. Before this I've always used IEMs, mainly the Shure SE530 which I've had for about 4-5 years now.
 
In my search for a decent pair of headphones, I've also tried out the KEF M500 and Sennheiser Momentum (over-ear). I loved the sound of the KEF, very detailed and spacious, but because it's an on-ear model the pressure on my ears would create great discomfort after about 2-3 hours, so I returned the KEF. I also like the sound of the Momentum, but again it gets uncomfortable for longer listening sessions, since the earcups are too small for my ears, making them a semi on-ear/over-ear model for me. I have to readjust them every 5 minutes, distracting me from the music. So that more or less also rules out the Momentum.
 
So, first of all, the P7 looks great. It's made entirely of black leather and metal, no plastic parts. I like the fit and finish of it. It comes with a small semi-soft carrying case. The P7 folds down into a relatively small package, so it's quite portable. It comes with two cables, one of them has a mic and iPod/iPhone controls on it. I installed the one without the mic and controls as I won't use them. The cable tucks away nicely, first giving you the impression that the cable isn't removable at all. But removing the magnetically attached earcups reveals the plug and then changing the cables is easy enough.
 
Comfort wise I really like these. I've been wearing them for 5 hours straight without any discomfort. The earcups are significantly larger than the Momentum, but I don't think they get too bulky. The clamping force will initially seem a bit strong, but for me that quickly disappeared after a few hours. But because of the weight you might feel a bit of pressure on the top of your head, since they're a bit on the heavy side for portable headphones. A wider headband would have been nice to distribute the weight more evenly. But it's not a major concern. I also didn't find my ears to get overly hot or anything, so overall they're quite comfortable.
 
Now onto the most important part, the sound. I tested these using a FiiO E07K DAC/AMP, connected to my laptop using a USB cable. Almost all of my source files are lossless (FLAC) and all EQ settings were turned off. Since I still have the Momentum laying around, I did an A/B comparison with the Momentum. I also let them burn-in over night and they've had about 15+ hours of playtime now.
 
A quick disclaimer, I don't consider myself an audiophile. I do really love music though, and I want my music to sound as good as possible. My hearing most likely isn't perfect, since I used to go to many parties when I was younger with the music playing way too loud and my ears ringing when I came home aftewards I'm also by no means a basshead, but I do like it when a headphone can produce a decent amount of bass when a song calls for it. I listen to a wide variety of genres, so I want a headphone to perform well with most, and I like it when they excel at rock/alternative, especially the midrange where you usually hear the guitars/strings (I love the sound of a guitar).
 
So, the main thing I noticed when listening to the P7 is the soundstage. It has quite a wide soundstage (though I've never owned an open headphone before, so wouldn't know how much wider it could sound), especially when compared to the Momentum. I feel like this soundstage gives more breathing room to all the individual instruments, so that each one of them can be heard more clearly without them constantly trying to drown out each other. I feel like the Momentum suffers a bit from this sometimes, because of the more intimate soundstage. The P7 comes close to sounding like an actual speaker, where the sound fills the room. This is something the KEF M500 also achieved, that big and full sound, that just sweeps you away.
 
One other thing I noticed was that the vocals are well defined and on some songs nicely separated from the other instruments. Whereas with the Momentum I sometimes felt that vocals blended in with the background a bit too much, the P7 separates it nicely while at the same time not making them jump out too much.
 
In terms of sound signature, it's actually a bit similar to the Momentum. It just doesn't roll-off the treble as much as the Momentum does and the bass has a bit more oomph to it. Still, the bass manages to stay well controlled. When I put them on the first time I could hear a clear mid-bass hump, but I feel that with the burn-in that has mellowed out a bit (or my ears have just gotten used to it). Also, I feel like the bass reaches a bit deeper on the P7, vs. the Momentum. It also has a nice sub-bass, which helps when listening to electronic music. The mids are actually quite gorgeous. Luscious is the word that kept coming to mind. Gorgeous and detailed. And the more present treble adds some airiness to the music and helps to create the wider soundstage.
 
Speaking of soundstage, I felt that the P7 has very good imaging. It's very capable of placing individual instruments left, front, right, back, even above and below. There is also a bit more prat with the P7 vs. the Momentum, which sometimes gives songs an exciting quality (and that's a good thing to me!). I find the sound overall a bit more engaging compared to the Momentum. Actually, it keeps reminding me of the KEF M500 in a way, which I really liked. It has some of the qualities of the M500 such as spaciousness, agility and that full bodied sound, but keeps the sound signature of the Momentum, which I overall preferred (especially with the vocals, I found the vocals to sound a bit thin sometimes on the M500). Do keep in mind that if you're looking for a neutral headphone, you probably won't find it in the P7, as the P7 is on the warm side of neutral.
 
What this headphone accomplishes for me is to immerse me in the sound and makes me forget what's going on around me. And since it's quite comfortable, I sometimes don't even notice I'm wearing these headphones. I know many people have complained about the small earcups of the Momentum, so for those people I'd suggest you definitely give the P7 a try, it might just be what you've been looking for
 
Update: One thing I forgot to mention is that the headphone isolates very well from outside noise. Earlier today the neighbors were drilling into the wall which made a hell of a noise, but when I put on the headphones with music playing at average volume I didn't hear a thing. In terms of leakage, I did a quick 'n dirty test with a mic at high sensitivity and it didn't pick up much of anything. So I'm pretty sure other people won't be bothered by it
 
Update 2: This P7 has a really great sub-bass, it reaches really deep. Deeper than the Momentum. On some electronic tracks I'm hearing basslines I've never heard before. And again, it's not overpowering, it doesn't drown out the mids or highs. I think it really helps to create a full-bodied sound and adds some weight to most music. The P7 is not a bass-head can, but if you like bass I think you'll like the P7. And you get luscious mids with good highs as well.
 
Update 3: With close to 30+ hours of listening time now, I feel like the bass has mellowed out significantly. At first when you put them on you might think the bass is a bit strong, especially the mid-bass, but now it's much better Oh, and I do think this headphone will let you hear the flaws in bad recordings, but it's more forgiving than the M500.
 
Update 4: Now almost 2 weeks later I still love the sound. The comfort, however, is another story. My left ear starts hurting after about 3 hrs. of listening. My right ear is fine, eventhough they're the same size (weird). The size of the earcup, or actually the space inside for your ears measures about 59mm long. My ears are 65mm long, and the average for males is apparently 64mm. You would think from an ergonomic point of view they'd design those things to fit the average ear. Anyway, in spite of how much I like how they sound, I've decided to return them as I want my headphones to be completely comfortable as well as sound good. So I've adjusted the rating accordingly, by dropping it a half star. Don't get me wrong, it'll probably still be comfortable for most people, as the earcups are siginifcantly larger than the Momentum. Just not large enough for my ears