From my understanding, the Plyr module is for integration with the Plyr video player, I don't think it supports MP3.

As it stands, from my brief research, UNA does not have an OOBE for MP3 files or any audio files for that matter.

@LoneTreeLeaf plyr definitely plays audio.

https://plyr.io/

I was hoping there was a setting somewhere for what files to preview with what player, etc etc.... Otherwise we are back to modify core. Lol