This is an odd way to start a review on a pair of Senn 595 headphones.  Nonetheless, I'll start by saying that I love my Denon AHD5000 headphones.  Weird start, eh?  So why am I looking at the Senn 595 headphones?  Well, my office listening situation has changed and I no longer need the isolation offered by the Denon's.  In fact, there are times when it is a problem.  Therefore, I've been looking for a new pair of open-back headphones for the office.
 
I have a pair of Senn 590's at home that I quite like...but I want to keep them at home.  I also have a pair of Grado 225's I occasionally enjoy, but are not a great choice for the extended amount of time I wear headphones at work.  Based on my fondness for the 590's, the generally positive reviews here, and a killer deal at amazon.com ($130), I decided to order and audition a pair of 595's.
 
Right off the bat, let me say that burn-in is very critical for the 595.  Each of my favorite headphones has benefited from a multi-day burn-in session.  So it's no surprise that the HD595 needed a break-in period as well.  The surprise is how shallow the improvement curve was initially.  The other headphones (HD590, Grado 225, Denon AHD5000) all started out lacking detail and impact, but after a few hours each at least started to reveal their *potential*.  OTOH, the 595's remained boring and flat during two straight days of continuous burn-in (interspersed silence MP3's every few hours).  It was only after 2 days that there was any signficant improvement and it took 3 days for the potential to start to emerge.  If I had stopped the burn-in at 3 days, I would have returned them.  However, it was the weekend (making it inconvenient to return) and by 4 days the 595's were close to the 10+ year old 590's in warmth and probably better in detail.  I'm now well pleased with them and they're not going back.
 
Comparing the 595's to the Denon's isn't a fair contest.  The Denon's are easily my favorites, even if the bass is occasionally overwhelming.  However, for some types of music the 595's might actually be better for my taste.  Diana Krall, for example, really shines on the 595 whereas on the Denon's you have to supress the bass to bring Diana's vocals and piano out.  In fact, I think I prefer the 595 for many jazz pieces and the bass actually a bit more detailed than the Denons.  On the other hand, throw on some Lady Gago or Daft Punk and I definitely want the Denon phones.
 
Compared to the 590, the sound is very similar.  My 590's are very old and worn...perhaps that gives the 595 a bit of an edge on detail, but OTOH the 590's are much much more comfortable.  The earpads on the 595 are a bit stiff and plasticy compared to the very cushion-soft 590's; of course, that might just be due to the age of 590's.  The 590 also has a detachable cable whereas the 595 has a fixed cable.  However, to make up a bit for that, the 595 does come with a very nice headphone holder that can clamp to a desktop, shelf, or bookcase side (about a $20 value).  I think I prefer the 590 overall, but it's not a huge gap.
 
Compared to the Grado, the 595 does not have the detail or clarity of the 225.  However, the bass (after lots of burn-in) is probably better on the 595.  Note that I have modded the Grado's with the circumaural "salad  bowl" pads from the GS1000 as well as a JMoney headband.  I did the comparisons with both sets of Grado pads.  The comfort is way way better on the 595 compared to either the original or circumaual Grado pads. 
 
Interestingly, even though the Grado probably has better sound quality, the 595 and the Grado occupy the same niche in my office rotation of headphones.  Because of the comfort offered by the 595, I'm going to use it (rather than the Grados) in rotation with the Denons. I am definitely enjoying these...after a good break-in period, of course.

(This is a repost of a review I did in the forums)
 
The Asgard has been on back order for about 2-3 weeks.  It started shipping again this past week and I just got mine this afternoon (1/22/2011) and I thought I'd add my own impressions.  Please go easy on me...this is my first ever review of an audio component and my first ever on Head-Fi. 
 
Customer Service...or Jason ROCKS!
Like others, I am stunned by the incredible responsiveness of customer service.  Certainly they have the benefit of a small operation and therefore an intimate connection to inquiries.  Nevertheless, we should applaud a company who answers an email question within 10 minutes on a Saturday afternoon.  Maybe I got lucky, but others have mentioned similar stories often enough that we have to just accept that they offer exceptional service and responsiveness.
 
Delivery time was also great.  They handed off to the carrier when they said they would...although I should note that the speed of the actual transit is the responsibility of the carrier (FedEx home delivery in my case) and not Schiit.
 
Accessories
As others have noted, the Asgard ships with a power cord, a 1/8" to 1/4" adaptor, a stereo 1/8" to RCA cable, and adhesive rubber feet.  The RCA cable is very thick and sturdy.  It is probably not the match of high-end audiophile cables, but its much better than the cables that come with most consumer electronics.  The rubber feet are small and shallow--they give only about 1/8" of clearance. 
 
I'm thinking about replacing them with some AcoustiFeet, which I like using for my computers.  They could have helped some of the mechanical hum that some folks have reported.  However, it's probably unnecessary...remember the speedy email response that so impressed me?  The 6moon review mentioned the low-level buzz issue as well as a side note that Schiit was already working on the solution.  I wanted to know if they had addressed it yet and Jason said that all units now shipping (they just came off of backorder last week) should have the fix.  I can say that my unit seems absolutely silent.
 
Sound Quality
I'm burning in the Asgard at home with a Senn HD590 and a Grado SR225.  Both sound incredible.  My previous amp was a Rega Ear demo unit that I bought at a steep discount from a local high-end stereo shop.  The Rega was definitely a huge huge improvement over using my PCs stock headphone jack (or at least it was once I found and corrected a faulty cold solder joint).  However, right out of the box I noticed vastly improved detail on the Asgard with both the Senn and the Grado.  I thought that the Rega had opened up huge detail, but the Asgard really blows my mind.
 
I don't know the terminology most people use, so I can't say what it is about the sound, but I feel a stronger emotional connection to my music listening with the Asgard than I did with the Rega.  I don't mean to be overly effusive, but some of my tracks sound as if the performer is running his or her fingers through my mind.  I'm listening to an Ottmar Leibert piece right now and it's so good I feel little shivers between my shoulder blades.  I keep finding excuses to come into the den for just one more "taste".
 
I can't hear the high-end roll-off that some people have reported.  However, I should note that I'm an over-40 listener and I have definitely lost some high-frequency hearing (I really can't hear that "mosquito ring tone" for example).  So it may be that there is roll-off occuring above my threshold to notice it.  Who knew that my impending decrepitude would be a blessing in disguise?
 
This amp is ultimately going to end up in my office where it will most likely be used with a Denon AHD5000.  I am really really looking forward to that!
 
No Snap, Crackle, or Pop
I really appreciate that there is no audible pop when inserting or removing headphones from the amplifier.  Same with turning the amp on and off.  This was a problem with the Rega.
 
Running Hot
Does this amp run hot?  Compared to the Rega it sure does.  I've had it running now for 5 hours (in the horizontal layout) and relative to the Rega it is very hot.  However, in an absolute sense its just very warm...definitely not going to cook anything on it.  I doubt it would even melt my daughter's crayons...not that I'm not crazy enough to try.  I come from the PC world, so I would say that it is about as warm as a low-end passively cooled video card.  I have absolutely no qualms about the amount of heat I'm observing.
 
Correction: I was checking the temp at the top of the case.  The bottom of the case is significantly hotter...I probably *could* melt a crayon against the bottom of the case.  Definitely going to find some bigger feet and/or setup vertically.
 
Criticisms/Feedback
I only have a few minor nitpicks to offer.  First, the Rega Ear has a set of passthrough RCA outputs with a manual cutoff switch.  This is great for PC use...I hang the Ear off my DAC and pkug my computer speakers to the RCA passthrough connectors on the Ear.  That allows me to easily enable or mute the external speakers while leaving the headphones plugged in full-time.  I will miss that but I'll deal...somehow...(cue violins)...
 
Second, I'd prefer it if the brushed aluminum case were finished/coated.  I like the current look but I'm not fond of the feel of bare aluminum.  Still, it's not a big priority for me.  I knew this from the forum comments and it didn't factor into my purchasing decision at all.  (Correction: I got PM from Jason and the cases are "clear anodized"...I think this was mentioned before on this forum thread, but I had forgotten).
 
Third, it would be nice to include some feet with more clearance.  Right now I have the Asgard lying on a pair of chopsticks until I can find my extra pack of AcoustiFeet.
 
Conclusion
I am very happy with this amp and I am pleasantly surprised at the low cost.  To me, this amp looks, feels, and sound much more expensive.  I would gladly recommend the Asgard to my friends and family.