Earlier quoted context omitted.
...a solution that has long been found in the music business. Perhaps you're fortunate that everything you want to listen to is on your preferred music streaming service, but what they offer is far from everything in the music industry's catalogue. Ask any classical music fan what they think of streaming services and you'll hear a tirade against the woeful offerings that streaming services make available.
This is why I love Google Play Music, you can basically upload any kind of personally-acquired (legally or not) music to the service and it will seamlessly and transparently integrate with the platform itself and let you stream them wherever and whenever like any other. They are stricter than Spotify with regional licenses unfortunately. I listen to a lot of Japanese artists that are on Spotify but not on GPM in Euro…
It's totally open source, has a relatively decent web player, allows you to stream your music anywhere, allows you to create accounts for others to have access to your music, can connect with Plex/subsonic to work with other devices/clients. I use DSub on my phone, and can sync music offline (like GPlay Music). Only downsides really is that it requires a web server and the initial import can take some time if your library is very large.