I got the free Nils Frahm Solo Album in 24 bit wav on Piano Day, still free available here: http://www.pianoday.org/ .
I converted this Album to lossless m4a files (alac) and placed them on the micro SD of my Pi.
I can see and play the files in musicbox, but with a odd skipping and stuttering. I can’t see errors in /var/log/mopidy.
I’m using a CM6206-LX based USB DAC.