The thing I liked about the dsp-500's is that instead of a sound (like footsteps) slowly fading in as someone approached, they wouldn't be that big of a difference in volume between when they first became audible at a long distance and when they were right next to me. I'm not looking for quality. I'm looking for something that is comfortable and will let me triangulate things at a good distance away. The only game the dsp-500's really stood out for me was counter-strike. Unfortunately, mine broke and they are no longer in production.
I've found that although analog headphones provide a better sound quality, they don't give me the same edge I had with the usb sound.
Find another pair of DSP-500's, I just sold mine locally last year. I bought another pair on eBay a while back before that.
You can also find them in a revised addition of GameCom Pro 1's as the name; and yes the Icemat's are still pretty good too.
Please don't listen to all these people raving about digital versus analog. In many situations it's preferable to have a pair of real cans with proper audio. In your case what you want is another set of DSP-500's. The ONLY issue you'll have is that the software that worked with it on XP will not work on Windows 7. However, Windows 7 will automatically recognize them and give you similar options (without the room effects) to the software such as bass boost, etc.
They might not, without the software that came with them and was used on XP operate in exactly the same way as Windows 7.