Riddle me this... Why would live TV have sound but recorded shows would not? It's the same tuner in the same myth box! Same line input too. (more about the tuner card)

Sound output works great for pre-recorded AVI and MPEG videos. Surround sound pass-through doesn't work from DVD, but I think that might be a separate issue. I have an asus M2NPV-VM and am using coax spdif if that helps.

If you're playing the recordings back with the builtin player rather than doing something strange one possibility is that live TV and recordings use different recording profiles, however, given that your card uses the bttv driver I'm guessing that the audio track is never actually making it into the recording for some reason.

Does your audio from live TV run slighlty ahead of the recording? Does it contiunue if you hit pause? If so then that's the problem.

Live TV had been behaving perfectly, as far as I could tell. But then I rebooted and sound stopped working for that too. Sigh.