The audio in the HDMI output can be muted using discrete (contact closure) input or RS-232 commands. The HD-AUD-IO is capable of generating an HDMI output even with no HDMI input. This can be used to ...

I could then put an HDMI switch in front of that to allow more devices to join the party. (Ideally, the HDMI switch and the HDMI audio extractor would be the same device.) ...

This is my first time dabbling with SPDIF/audio extraction (previously have been 3.5mm/RCA/HDMI pretty exclusively) so here I am posting before clicking the buy button on anything.