kirkmc

I tried, and, yes, it isn't apply Sound Check corrections. Playing a soft and loud track isn't necessary. If you select a track and press Command-I, then look at the File tab, you'll see the Sound Check correction in dB. So what I did was play a few tracks with Sound Check off, and I recorded them with Audio Hijack. I then played the same tracks with Sound Check on, and recorded them, and simply looked at the waveforms to see the difference. So Airfoil is one option, and you might also want to check out Rogue Amoeba's Loopback, which should also allow you to do that. (I haven't tried it.) Since I never use Sound Check - it sometimes results in noticeable artifacts - I'd never noticed this before.

How do you verify this? Do you have music where it's obvious when Sound Check kicks in?

I don't see why AirPlay should have any effect on Sound Check. I don't use it currently, but have in the past; I stream from my iMac to a Sonos Amp in my home office. If it's not working, then that's clearly a bug.

By "merged" do you mean moved it to the new Mac? I've got some that I've moved from my iMac to my laptop that still don't display. It's frustrating, and I don't know why.

When I upgraded to Catalina on my iMac, it took a couple of days for the artwork to display. I don't know why it takes so long, but I've heard from a lot of people with the same issue. Leave the new Mac mini and the Music app running as long as possible.

For a while, iTunes would download both SD and HD versions of movies, but that stopped some time ago. But two copies of music files is a bug.

If Cloud Music Library is on, then both will be in the library, and will be playable from anywhere. I don't know why the OP is getting two copies; just delete one of them.

Artist images have always been weird. Sometimes, iTunes/Music just gets stuck. Try removing the Aretha Franklin tracks, quit the Music app, then launch it again. Let it go and see if it updates. Then add the music back and see what happens. It could be some corruption in the database, or in the existing artist artwork.

So if you're not using Music, why do you have music in its library? Also, if Music is opening, and the setting in System Preferences isn't working, do you have any disc burning software that may have installed a driver that could be opening the app?

So you're no longer using the Music app, yet it's updating images? What exactly does that mean?

The Music app copies all the files to the location of the folder set in the preferences. You can then delete the other files that weren’t in that folder (though do keep a backup until you’re sure that nothing is missing). The point is to consolidate the files in one location.

Why do you have two music folders?

My guess is that it has something to do with the sound output failing. If the Mac doesn't recognize the Toslink connection, then that suggests that it's not just the analog sound, but the entire connector. It may or may not be difficult to repair. Perhaps try and see if you get audio out via USB, to see if it's something deeper (ie, a software fault that could be fixed by reinstalling the OS.)

As I said, the files weren't added. So you re-added them. I think you could have just done that without spelunking and you would have saved some time. (To be fair, you may have a lot of time on your hands right now...)

They got added to your Mac, but apparently not to the Music app. So just re-add the files to the Music app.