Looking at your sig it says your using Realtek HD Audio 2.90 beta. I've never heard of that driver as the newest driver I know of is the 2.49 that you can download here.
Realtek HD Audio 2.49 Driver download from Guru3D.com
I also looked at the MSI site and there was an older bios that updated the audio table (whatever that means), it was bios 1.2. Any newer bios should contain that update already but if your new mobo was on the shelf for any period of time it may not be updated.
Edit: The link MoM supplied is to Realtek's website in Taiwan, it's slower than slow. The Link I supplied is a High-Speed Download