To make any music player that comes with sound indicator integration the default player in there we may from 13.04 install and run unity-tweak-tool . Open the "Panel" settings and choose any of installed players:

The example above will then make Guayadeque the default player in the sound indicator:

Of course if we prefer not to install an additional application, or if a player such as Quod Libet does not come with full indicator sound integration we can also do this with dconf-editor (from dconf-tools in Ubuntu < 13.04):

Quod Libet need the MPRIS plugin (quodlibet-plugins ) for full player control.