This is exactly the problem that http://toma.hk http://toma.hk and http://www.tomahawk-player.org http://www.tomahawk-player.org are trying to solve. Their app

This is exactly the problem that http://toma.hk http://toma.hk and http://www.tomahawk-player.org http://www.tomahawk-player.org are trying to solve. Their approach: your library becomes (title, artist, album) tuples, and then songs are found at whatever provider you use when you want to listen. The devs are mostly ex-Amarok and everything is on GitHub: https://github.com/tomahawk-player https://github.com/tomahawk-player.