ASUS Xonar Essence STX - Headset?

Any high impedance headphone would benifit from the STX's muscle.

Problem is, they tend to cost an arm and a leg...For example, teh Sennheiser HD 600 costs ~$500 or so, though there are cheaper options...

Hd650 cost 350USD

http://www.amazon.com/Sennheiser-HD-650-Headphones/dp/B...

^^ Thats what I get for looking directly at sennheiser's website, where the 650's cost >$800  

Sennheiser HD-558, go to the Electronic Expo website, when buying the HD-558, use the coupon code "BOUNTII"

Well, I'd really like it if you could find anything with a microphone attached to it, like the PC 350 / 360

astro A40 w/ optional mixamp (there's also a wireless edition, but I haven't tried it) is the best out of the 5 or 6 high-end models I've used.

http://www.astrogaming.com/

Have the exact soundcard. Do you use the headphone output on the back of the card?

For music, I have Senn HD650, Gaming, Razer Carchrias

http://store.razerzone.com/store/razerusa/en_US/pd/prod...