Sorry for the late reply.
Your copies of Rhythmbox don't export the MPRIS dbus interface which is needed for the sound menu to discover and manipulate media players. Do you have the MPRIS plugin enabled?
Sorry for the late reply.
Your copies of Rhythmbox don't export the MPRIS dbus interface which is needed for the sound menu to discover and manipulate media players. Do you have the MPRIS plugin enabled?