Heh, I had been pulling my hair out over the fact that my TV monitor no longer played sound when I hooked my BionicPup64 laptop to it. Video was fine. Just no sound.
It had worked fine before that, then suddenly sound was gone. I checked that I'd enabled HDMI in the Multiple Sound Card Wizard. Check. All levels looked good in Retroval. Check.
If I switched back to Analog sound on my laptop, that worked fine. Both speaker and headphone were loud and clear. What could be the problem?
Finally I installed another instance of BionicPup64 -- and HDMI sound worked fine there. But I didn't want to recreate everything from scratch on a new savefile. I wanted my old pup savefile to work with HDMI, as it had for a couple years.
Finally I noticed one small thing that I usually never paid attention to in Retroval. That was a little checkbox labeled "IEC958". It was unchecked in my old savefile, but it was checked in the new one.
And that was the problem. IEC958 is apparently a digital sound protocol between two sharing devices. In order for my TV to receive sound via HDMI, it needed IEC958 to be enabled.
I checked that box in my old profile, and presto, HDMI sound returned. I have no idea how it got unchecked -- maybe an errant keystroke. But that was it.
So, seemed like I might not be the only one with this problem, so I figured I'd write it up here.
Hope it solves a problem for you, too.