Depends what you need from the soundcard.
If you're just looking for higher quality sound than on-board sound you don't need to spend so much money.
The much higher end cards only really offer you hardware accelerated 5.1, 7.1 sound, which is useless for headphones.
I play FPS games through your average stereo USB DACs and the software audio does a good enough job of positional cues etc.
I would only get such a soundcard if you really need all the whistles and bells that they have to offer in the bundled software and you want the extra hardware acceleration.
Otherwise even a simple USB DAC would suffice.
I use one of these at work - http://www.ebay.de/itm/PCM2704-USB-DAC-to-S-PDIF-Sound-Card-Decoder-Board-3-5mm-Analog-Output-/201089065014?pt=Wissenschaftliche_Ger%C3%A4te&hash=item2ed1d7a036
(although it took about 2 weeks to get to Germany)
For my vintage 600 Ohm Beyer DT990, I need to put the system volume to 50%, otherwise it's too loud.
It sounds great too. Totally silent background (no hissing even at max volume with IEMs).