I was reading another thread (Solved - No audio as service but sudo -u mopidy works (DietPi)) and it made me think that maybe it was just a permissions issue for the mopidy user.
My test bed system is now seeing the CD just fine. I’m going to be a little more judicious with my “production” system (I added mopidy to the video group as well as the cdrom group - I think just cdrom will do.
I’m very excited about this. Thanks to everyone, especially afpeluso, for the input. Now if I can get Iris to give me control routing audio from different snapservers to different snapclients (another issue that I’m sure is user error on my part) I’ll be absolutely thrilled rather than just happy.
Added: “sudo adduser mopidy cdrom” fixed it. The “production” server can now play back a CD, which isn’t necessarily a huge deal for a lot of people, but it allows a bit of spontaneity to the whole thing.