It is a good sound card, and sounds like you are getting a good deal on it. Sound cards don't really go through much stress so it should be performing as well as a new one unless the previous owner was using it extensively (Way less than a used GPU/CPU; you probably won't be able to tell the difference between this sound card and a new one).
I have this hooked up to my Z-2300s on W7 Ultimate and I absolutely love it. The sound sounds amazing and crisp. I'm not an audiophile, so my opinion is a bit less developed than most people here, but I would get it.
No problems with mine on Windows 7 x64. Installed drivers without issue. Only paid $109 at Best Buy for it, last month. Very awesome sound card for gaming (and movies). Made my aging Logitech Z-2200 system come to life.
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