Not much info in the service manual.
Yes ,of course on vcc & ground.

AN 2 & 3 appear to be only ones active. DACC likewise only one active.

Audio is spread across main board and left board, not in accessory card itself.

Sense "VESense" and xrst are tied to "control bus"
Rxd & txd are tied to Midi bus.

So, switch pins 3,4,7,8,9,10,13-20 & see what happens.