Honestly, adding a "Play next automatically" checkbox to the "playmusic" page (e.g.
http://www.contrebombarde.com/concertha ... usic/17824) would quite possibly get you 95% of the way there.
That being said, I am not a web programmer and have no idea how hard this is
I might also worry a bit about the effects on the community. The song ending and me needing to click to the next one is also my prompt to comment -- I might not comment as much if they all just play through!