Q. I just installed the nVidia nForce UDP v.2.00 driver package but I don?t have any sound. What?s wrong?
A. ASUS has a customized version of the MCP-T southbridge. They added a few extra features to the APU, which required them to change the device ID's of the APU. These drivers do not have these custom device ID's in their INF files so the drivers do not get installed. The drivers are fine to use, and work perfectly with this board, however you must install them manually. Open your device manager by right clicking on My Computer>manage>device manager and installing the drivers manually for all the sound devices in your system. Recently ASUS came up with a version 1.16 package, which despite the lower version number, is actually newer, then the 2.00 package and it is recommended you install those as the custom device ID's are no longer and issue and manual installation is no longer necessary. These drivers also resolve other issues, some of which are outlined in this FAQ.
This is taken from the Asus A7N8X FAQ and may be the cause of your problem. Also do you have the deluxe version or the normal? The Deluxe has a better sound solution on it the Soundstorm while the regular one has a basic AC97 sound card.