I have recently completed two new HTPC builds....both with Gigabyte 780g mobos but not the same versions.
I am using the on board video and audio for both.
I installed x86 RC1 on the first build and WMC has no audio issues other than I can't get HDMI audio on the Realtek to work (similiar to what others have posted).
The real problem showed up last night when I finished the new build and installed x64 RC1 to tale advantage of the extra ram.
No HDMI audio again so I hooked it up via spdif out.
Seemed to stream web radio OK outside of WMC but when I opened WMC there was a bit of stuttering and playing the included audio file was brutal. Stuttering and static.
Is x64 not as ready for primetime as much as x86???
I installled the new Realtek driver
and it didn't help. Also...still no audio over HDMI as well. No way to activate it in the control panel.
I may install x86 instead tonight.