I currently have the AD700 - which I have really enjoyed.  However, I've been looking to upgrade a bit.  I originally got the AD700 because of it's highly extolled virtue in gaming (positional sound) coupled with it's relatively high quality compared to most "gaming" headsets.  To those ends, it has treated me very well.  I really enjoy the wide open feel of them, and the comfort levels is great (after the rubber band trick - these things are huge).
 
I'm looking to in the range of $150-250, considering the following:
 
K702
HD598
AD900
 
For sound on my PC (where it is most often used), I either use an X-fi card or my FiiO e10.
 
I've been reading up on the forums and the like trying to get a handle on the differences between the three I'm considering.  From what I can tell, it sounds like K702 requires amping.  Would the e10 accomplish this well enough?
 
I'm looking to have a large, accurate sound stage to, at the minimum, maintain the gaming prowess - but of course this is also a boon for music.  Essentially looking to move up to a fuller sound.  Do you guys have any suggestions on a good all rounder, considering I'm upgrading from AD700 with about a 50/50 mix of music and gaming?
 
Feel free to drop some alternatives as well, I'm open to suggestions.
 
Thanks!

Edit:  Just realized there is already a recommendation thread!  Sorry for cluttering - I'll post in there instead.

Heya,
 
I would start pointing you towards:
 
Hifiman HE-300 (rev 2)
AKG Q701
Beyer DT880
Denon D2000
AudioTechnica A900X
 
Your E10 would do fine for all of them.
 
Very best,