I'm using a pair of AKG K242 HD (stereo headphones) myself together with the Dolby Headphones feature of my ASUS Xonar DX and I get a
much better surround experience compared to my friends 7.1 USB headset. Surround gaming headsets are primarily a gimmick because we don't have seven (or five) ears. We pick up sound from multiple locations to two microphones (ears) and latency, volume and sound pressure determine where the source is located. This can be replicated with stereo headphones (emulated) much better than a 7.1 headset can. Check out this video for a more detailed explanation:
http://www.youtube.com/watch?v=SQmQD27uCt0
You could just pick up a
USB soundcard and it would essentially turn it into a "USB headset".