I’ve had audio dropouts with NVIDIA cards before and in my case it didn’t matter whether I was using audio passthrough or having the computer decode to PCM. However, it did seem to matter the video that was displayed. I could most reliably reproduce it with a video file that had periodic black screen with some white text (intro credits). In my case, changing the power control in the NVIDIA settings resolved it: HTPC Tips and Tricks - #5 by gbooker02
Hopefully this will help you as well.
