[ScaryFatKidGT]

So I own D5000's which are my favorite, SE215's and 535's, V-Moda M80's, Beyer DT 770 80ohm, Momentums, but the only open pair I have are my Porta Pros lol.
 
Every time I look at open headphones I get confused as they don't have great reviews but then anytime you read close headphone reviews they always say they have issues because they aren't open and there for have issues with the sound caused by being sealed.
 
I have a $200 gift card to Bestbuy so I have been considering the HD598/600/650/700's that the Magnolia store sells. Now I'm after something a little better than the 598 but at the same time I don't have an OTL tube amp and I have always thought of the 600/650's as smoother and slower for classical and jazz. I listen to more upbeat rock and metal usually, along with some slower folk/rockish stuff and electronic.
 
The HD700's are faster and clearer, but most of the reviews I read on them are very mixed and with the gift card would be the most expensive I could afford.
 
Beyer DT880's or T90, these aren't sold at BB and would be all out of pocket cost, however I'm liking the T90 as an option.
 
The last and maybe most promising I have found are the Philips Fidelio X1/2 and L2's. The main issue is I'm not quite sure what the difference is between the L and X series, both are open/semi open mid-high end audiophile over ear headphones...
 
Also I'm not sure but I might prefer the X1 over the X2 but I would have to listen to both, and the L1 I guess to really tell. Most of the reviews I have seen on these are rave, everyone seems to love them, saying they are even better than the HD600/650's.

 

[PurpleAngel]

  So I own D5000's which are my favorite, SE215's and 535's, V-Moda M80's, Beyer DT 770 80ohm, Momentums, but the only open pair I have are my Porta Pros lol.
Every time I look at open headphones I get confused as they don't have great reviews but then anytime you read close headphone reviews they always say they have issues because they aren't open and there for have issues with the sound caused by being sealed.
I have a $200 gift card to Bestbuy so I have been considering the HD598/600/650/700's that the Magnolia store sells. Now I'm after something a little better than the 598 but at the same time I don't have an OTL tube amp and I have always thought of the 600/650's as smoother and slower for classical and jazz. I listen to more upbeat rock and metal usually, along with some slower folk/rockish stuff and electronic.
The HD700's are faster and clearer, but most of the reviews I read on them are very mixed and with the gift card would be the most expensive I could afford.
Beyer DT880's or T90, these aren't sold at BB and would be all out of pocket cost, however I'm liking the T90 as an option.
The last and maybe most promising I have found are the Philips Fidelio X1/2 and L2's. The main issue is I'm not quite sure what the difference is between the L and X series, both are open/semi open mid-high end audiophile over ear headphones...
Also I'm not sure but I might prefer the X1 over the X2 but I would have to listen to both, and the L1 I guess to really tell. Most of the reviews I have seen on these are rave, everyone seems to love them, saying they are even better than the HD600/650's.

 
I'm going to make a (wild?) guess that as you already have the Denon AH-D5000 headphones.
It's going to cost a bit to find something that sounds noticeably better.
And Bestbuy already has high prices.
 
You might do better to sell off the $200 Bestbuy card and look for something mail order.

 

[DivergeUnify]

I cant think of a better starting pair than the HD600s. Best Buy has them. Theyre affordable, versatile, very well-received. Theyre what, 15 years old? Yet still reccomended all the damn time

 

[brandonlyz]

If you want a fantastic "pop" to your music with a fun sound, do try the DT990s. They have a big wide soundstage with incredible bass, extremely analytical sound. However, for a safer option just go with the the 600 (neutral) or 650 (slightly warmer + more bass) from sennheiser.

 

[money4me247]

Switching to open from the bass-heavy (not in a bad way) D5000 would be a noticeable change in sound signature/frequency response. I agree with PurpleAngel's comments that it may not be worth it.
 
If you are trying to find an open pair of headphones from Best Buy specifically within the $300-$500 that has a warmer sound signature, I think the HD650 ($409 via their website) or the DT990 ($379) or the Philips X1 ($335). Note that you can find all these cheaper on Amazon. Also, the X2 is currently out as well (though not available at Best Buy).
 
The only other "warmer than neutral" open options beyond what you already mentioned within your price range I personally can think of to recommending would be the Hifiman HE-400 or HE-400i or AKG K712. My personal "best value for sound" recommendation for open would be the Massdrop AKG K7xx for $200, though not available now (and will probably not be dropped again until at least after February).
 
All these headphones are great open options, just really depends on your personal preferences. You should try to demo some of them if you can to help make your choice.

 

[Porteroso]

Sell the gift card. Save some money.