The ALSACAP results suggest that some program is grabbing exclusive control control of your DAC and not releasing it. Are you running any other software at the same time? Do you, for example, have a browser open that's been used to play web audio or has a youtube video paused or something? Are you running a program like Audacity for recording? If you start MC right after boot (before starting any other software) and try ALSACAP (or try to play to other devices) do you get different results?
Another user saw a similar issue with a different DAC recently, and it would be interesting to find out what the issue is. What desktop environment are you using on Debian 10 or 11? Gnome? KDE? Something else? The fact that it works on Volumio, but not Debian suggests there's something in the installed environment that's messing things up.
For what it's worth, my SMSL DAC (the SH-9) works just fine with several machines using Debian 10 (running the vanilla debian versions of Gnome or Xfce4), and I've never seen an issue like you're describing, except once briefly when running Audacity at the same time. But I'm pretty sure something in your software environment other than MC is creating this issue.