When I'm using the exclusive mode for my HDMI port, the RAAT Server limits the channels number from 8 to just 2. I'm using Roon Server on Mac mini M4 Pro with Arcam AVR850 connected.
Welcome to the forum! I am reviewing the details you posted here and I was able to locate an existing development regarding this behavior. We are looking into this and it is in our queue, but I am unable to comment on a timeline of when exactly this feature will be added.
To help push this ticket forward, you are also welcome to submit a feature request in the below section, as our product team keeps a close eye on this section regarding what to focus on next: