Well I have been using mine for a week or so now.
I am no audiophile and I purely bought this as I game and I normally always use headphones (Creative Fatality Mk2's).
I was using a Creative Sound Blaster X-Fi Xtreme Audio earlier this year until I built my new rig. I found that the onboard on my Crosshair IV sounded a hell of lot better than the creative card, so started using that.
The ASUS DG, in my opinion, is a bigger step up from the above. I was amazed when I started using the onboard as I started hearing things in BC2 that I had not heard before.
The same has happened again. I am hearing yet more that I never knew was in the game.
For the money, this is probably one of the best upgrades I have made. I installed it no problems on Win7 64 and the driver programme is a doddle to use. It has so many different things you can tweak.
My mates have said that I sound a lot clearer in Vent, and I can also hear them a lot better.
My only gripe is that a couple of the capacitors were a little crooked on the board (I have put pics up in this thread), but the card is working like a dream.