I currently use Jellyfin with the Gelli App from F-Droid. It does support downloading complete Albums to the cache but you can't navigate your music library while offline so this doesn't seem to be very useful (only to save data if you have a metered connection)
I used to use gonic with Ultrasonic as a client app but as I have Jellyfin for video files anyways I don't host this anymore. This setup did support offline playback though and is pretty lightweight so it might be worth a look for you.
It is preinstalled and precompiled on ubuntu so you don't need to use dkms to compile the module. IIRC you can even use zfs as root filesystem right from the installation.