The external Music must be connected to an Analog extension port (SLMA..)
The Impedance of the music source for best results must be 600ohms.
The analog extension port must be programmed as follows
ADD-SSC:1-2-43-23,EXTANN,MUSIC,0,G711&G729OPT&ML&VIAHHS;
Then you just have to connect the music source output to the extension on the MDF, and that should be it...