I've looked at the asus website and they don't have an audio driver out yet for windows 7. I have tried using the windows xp and vista one just to see if those would work. Neither did.
The problem I am having though, is that I can only use my Left and Right front speakers, I can't use my C-Sub or rear speakers at all. When I run the windows 7 sound wizard or whatever I can click to test the speakers and I hear the sound coming from them so I know that they are working but nothing else will play on those speakers.
Currently I have uninstalled all of the asus audio drivers so I'm just running whatever came with windows 7 ultimate.
Have you tried googling to see if anyone else has released drivers for W7? I kind of doubt it, but possible.
I had a problem similar to this where my audio drivers crashed, eliminating all subwoofer frequencies. It took me a long while to figure out that the drivers and software package had to be completely reinstalled in order to fix it. It happened one more time, but I have yet to see it fail after that.