You can also insert a radio with a Pages Ext. page in the forum.
With this solution you have no performance loss in your forum
Also, you can't get any problems concerning any rights, because the music is not played on your forum page(Provided you choose reputable radio providers).
You just have to check from time to time if the external player of the selected stations still works or if the link changed somewhere.
Backgroundmusic that someone doesn't like to play in the forum can also be annoying.