You are referring to Quasar Media Player, which was a front end to mplayer most of the time. There never was support for Xmms. Also Quasar Media Player is no longer being actively developed. There was another thread with a Diablo and Freemantle port of Quasar Media Player: http://talk.maemo.org/showthread.php?t=30901

This thread is about QuasarMX, the successor of Quasar Media Player. QuasarMX does no longer use external applications like mplayer as back ends. It uses several internal back ends, including its own portable Meteora back end or Phonon and Qt Multimedia, both of which use GStreamer on Linux.