Keep your CPU2 card - it is better.
If this is only happening with the TiVo, I would blame it then. I have multiple multichannel sources at home, going to many stereo zones and have not heard this problem even once.
The TiVo might be switching to LPCM when you pause, possibly you could foul it by removing LPCM from the input card edid (if that is even an option).?
