Mpd + a frontend of your choosing, I prefer ncmpcpp, will run on just about anything and is remotely controlled through apps or ssh. Mpd is great when the server is physically connected to the audio output device. I use it to remotely control a speaker connected server that can also run Plex (because I prefer plexamp for streaming and syncing to my phone, other android devices, and smart speakers). They both look at the same directory of a collection near 30 years in the making with hundreds of thousands of files and a wide array of formats.