Definitely an odd problem. 1.
Definitely an odd problem.
1. Tune to a non-AC3 (Dolby Digital) audio program. These will have MPEG audio and WMC will decode to stereo PCM. Is the result the same? It may actually work properly because you may have not been bitstreaming to the TV as they often only accept PCM.
2. It is possible that perhaps there is some strange HDCP event happening so you could go on trying different cables as well as trying the video out to TV and audio out to AVR using separate cables. I’m not sure the exact capabilities of the board you have so you may actually require a second test GPU to try the dual cable approach.
3. Have a backup plan of getting a different vendor’s AVR or system if all else fails. Sometimes there are strange incompatabilities with HDCP if that is what the cause ends up being.