Heya,
Guys, he just said Dnb, Dub and Techno. How can anyone recommend the AD700 here? The word gaming automatically brings in that copy & paste junk doesn't it? Ugh man. Seriously. No. OP: AD700 has no bass. You will hate it for your genres. It's like butterfly farts in your ears for bass. He didn't even mention if he likes immersion games or competitive online-fps-footstep-listening games even. Absolutely nothing. And of course, here comes the standard "AD700!" recommendation copy & paste automation responses of the internet. Ugh man. Headfi can give you a headache some days.
OP: Based on your musical preferences, here's some suggestions:
Beyer DT990 PRO (open)
Beyer DT770 PRO (closed)
Fischer Audio FA-011 (open)
Panasonic HTF600 (closed)
Ultrasone HFI 580 (closed)
Shure SRH440 (closed)
Sennheiser HD449 (newly released; closed)
Denon D2000 (used if possible to save $; closed)
*Bolded are simply my recommendations for your overall situation.
As for a sound card, get something with Dolby Headphone. The Asus Xonar DG is a very inexpensive option. The Xonar STX is a more expensive, but more capable and higher quality option if it fits your budget. The Creative Titanium HD is actually a good card, and would suit your needs as well. I would suggest trying to get the Xonar STX if budget allows.
Very best,