msi kt3 ultra
This may help...
I have that motherboard and had similar problems. Turns out the driver that msi.tw listed a few months ago was different from the one that is there now for the on-board sound, or maybe the route to searching/clicking to it may have led to different files...or maybe i downloaded the one from the german site... I had real problems getting to their main/english site for a while at the time.
Anyway, I use the Realtek AC97 audio driver. There was another driver that wasn't labeled Realtek, and it worked for the on-board sound but I had crashing problems and getting it to recognize my rear speakers was an issue.
After getting the Realtek AC97 drivers on, I also turned down the hardware accel in sound properties, since it was chirping a bit while loading some games... Regardless, I just updated my drivers from their site and it works, so if you haven't done the driver update dance...this might help.
Oh, and fyi..many flavors-- KT3, KT3 Ultra, KT3 Ultra ARU, and KT3 Ultra2 which may have different drivers for the onboard stuff. Mine is the KT3 Ultra ARU 6380 E