Hmm, must have got mixed up somewhere then if I'm remembering open backs.
I play Fps a lot, Got Star Citizen so that'll have some fps and ambient simulator type stuff.
AKG K550s are closed, higher ups are all open as far I remember.
Like lots of higher up models of all makers.
Unless priced higher in UK Beyer's DT770 would be surely candidate with good price to performance ratio.
Not the widest soundstage but good for closed design of especially that price.
For FPS games you need good binaural simulation.
SBX Pro Surround is best balanced in that.
Old CMSS-3D wins in details, but kills bass and that fun immersion part.
Dolby has bloated bass from echo of everything.
If there's no feeling of good space (distance) and direction in listening that you know headphones are bad for gaming.
(or head/ear size and shape differ lor from average)
Outside that most sound cards would be actually likely indistuishable from each others in scientific testing.
Any kind testing knowing candidates is simply never completely free from psychological biases.
http://www.tomshardware.com/reviews/high-end-pc-audio,3733-19.html
Though of course there are clearly scientifically measurable things for certain cases like possibly headphones need more current than available (possibly clipping signal) or running out of voltage swing of output limiting volume and possibly interactions between output and heaedphone impedance.
And of course interference/noise in integrated sound cards, though that's actually mostly problem with low impedance headphones.
You don't say what your budget is or what their primary use will be but at the lower end you could get the Beyerdynamic DT770, which comes in 32, 80 and 250 ohm versions. Not a bad headphone and very popular but the highs are a bit strident for my tastes..
Dropping 8 kHz around 3-4dB in equalizer of any sound card should tone it down lot. (same for DT990)
It's better and safer to tone down some peak than try boosting something weak, because of no danger of signal clipping ever that way.
(like in trying to boost weak bass lot)