Hi Lance,
Fellow user here
Just to be sure I understand…
You are running the Roon Client software on your mac Mini and when you go into the Settings/Audio options, while on the Mini, you do not see it as Audio Endpoint. And, in the MacOS settings, the system output is enabled and works with other software programs.
If so, then the first thing I’d try is…
In order for RoonSErver to build the endpoint zones, it needs to be able to talk to your endpoint. If it cannot, then it won’t create the necessary endpoint zones. As a test, try turning off any firewalls/AV on the Mac Mini to test if they are blocking this communication. If it appears as an audio device, then you know you need to set exclusions in the firewall/av to allow RAAT/RAATSERVER/Roon.
If that doesn’t work then it might be related to this…