Ignore wickid. Logitech has few audio products worthwhile, the only one I've seen that looks good on paper is this:
http://www.amazon.com/Logitech-Transporter%C2%AE-SE-Network-Player/dp/B0011YZ1R6That's not exactly something you would use on a PC to play games.
Back to reality, stay away from Logitech and anything branded Fatal1ty. Both are hyped to gamers with aesthetics such as molded plastic and LED lights. Fatal1ty branded products aren't "bad" but the only thing they do is fill Jonathan Wendel's pockets with cash. The real question here is, do you want to be a typical AA player (sound whore, distorting realistic sounds to have bloated ear-damaging highs just to hear enemy at unrealistic distances) or do you want to hear things as intended?
I'll guess and say you want the latter; quality. What you really need is a good DAC and a sound card with a headphone amplifier. The X-Fi is great for screwing with equalizers but has low quality components onboard and no headphone amp, just regular headphone output. To get the most out of headphones (even IEM's) you generally need an amp. That ASUS Xonar D2 looks good but I can't help but feel it's overkill and is geared more towards home theater setups. If you're looking at that price range, maybe check out the ASUS Xonar Essence STX:
http://www.head-fi.org/t/421890/the-xonar-essence-stx-q-a-tweaking-impressions-threadThere's also HT Omega Claro cards that have great reviews.
But, if you're not going to go the home theater route, it doesn't make much sense to pay for all those features. There's other solutions as well. The NuForce products have been pretty popular and they're a no frills type. There's all kinds of ways to go. Maybe lurk around here for a while:
http://www.head-fi.org/f/46/computer-audioThere's a lot of setups and reading about products other people like might help you find a direction that suits you best.