paras the hd-555's aint good for gaming..
Neither will the ad-700 be good.. im sure i can ans ur question but would like to know if you gonna use the cans on the pc alone or will you use it for multi-purpose... i.e, with amps, pmp's, etc etc
The reason for asking you this is, that if its only for pc and nothing else then skip the audiophile headphones like the hd-555 or ad-700 or anything else and go for proper 5.1 true surround, powered by usb run headsets.. They will throw you back by around 7-8k but results are way better then the normal cans on the pc..
And YES, a decent sound card is required for better results as they will have 3 or 4 pins for front, rear and centre... Like i said, true surround..
Something like the turtle beach..
Steel series produces virtual surround if im not wrong//
Let us know