Thnks, it didn't even occur to me to try TOSlink. I do indeed want multichannel, 7.2 is ideal but 5.1 at a minimum
The unit you linked is a good example of why I'm having a hard time finding a solution - that converts the signal to ethernet, so I'd still have to run a Cat5e+ cable. If it goes over IP, I can do it wirelessly and apply QoS, VLANs, etc. as needed. When I search for something like 'HDMI over ethernet' I get dozens of those converter boxes but maybe 2-3 ethernet-over-IP solutions, all of which appear to use broadcast/multicast which doesn't mix well with a home LAN.