http://groups.drupal.org/art-music - seems like the main
http://groups.drupal.org/openmusic - interesting but not very active
http://groups.drupal.org/node/21648 - Crazy thread that goes from a dicography module to Drupal for Music Distribution (MD4D) to nothing.
http://groups.drupal.org/node/21648#comment-75633 - related project outline TODO: read
http://groups.drupal.org/node/18936 - Kendra Hub project proposal. Music distribution enabled artist sites. Need to learn more, continue reading from "How will you implement and distribute your project?"