McIntosh Amplifier (under drivers seat), has 13PIN DIN Connector/Cable to McIntosh head unit. Neither subaru or mcintosh could provide the pinout and signal level information for this connection.
I buzzd the connector and it appears to be 4 channels in differential pairs (no common), a remote trigger and ground.
AMP p5 GND p6,12
RL- p8 RR- p13
RL+ p7 RR+ p11
FL- p2 FR- p4
FL+ p1 FR+ p3
Then playd a sine wave at a few frequecies through the head unit. Unfortunatly it doesnt appear to be standard line-out levels, so a preamp might be required.. but i might get away without it. TBD.