I manage my music with iTunes because it can manage smart playlists that are created from other smart playlists. Every year or so, I go and look to see if anything open source has a similar capability, and nothing else does.
There are also a bunch of programs that have been created to help sync iTunes music and playlists onto an Android phone. DoubleTwist is popular, as it came bundled with a number of phones around 2010. Personally, I use iSyncr, which is a paid App on the Android side, but I found it works quite reliably. Sadly, none of these will sync with another computer, like a Rapberry Pi.
In any case, I've given up looking for something to replace the multiple levels of functionality that I get out of iTunes. The one single issue that I was trying to get fixed, I finally just wrote a program to do.