It looks like there might be a compatibility issue between my Oppo 980H and the VSX-01 over HDMI. When I use an optical audio connection, the listening modes work just fine. So not sure exactly where the error would be occurring, but I guess I'll just have to use an additional audio connection or stick to regular two-channel when listening to music (which I admit isn't often with this setup).
The cable box has me stumped though. This doesn't make any sense to me, but the listening modes only seem to work on one particular cable channel - when I switch to any other channel I don't hear anything out of the surround speakers.