I think BC9500 is the same (TV AUX pin 6 connected to MCL speakers). So the data going over an MCL system is Audio Aux Link (AAL)
Probably that is. However on any product diagrams they are lead to different pins on the microcomputer in the product. This could of course be for other reasons like not passing a standby all signal through the entire system chain, but only to components in the same room.