As it’s an ACM. it’s very likely that the channels have post-fader buffer amplifiers, and that’s the place to take your direct outs from…. either from the top of the fader (if you want a pre-fade output) or from the output of the buffer amplifier via, I suggest, a series R of about 680 ohms, to avoid loading issues.
I can’t really help further than that; that was a long time ago and I don’t have any records of the circuits, only some memory of how I did it in those days!
Those ACM mixers were the peak of audio excellence; they were built to absolute highest broadcasting spec and were the equivalent of the Neve and the Calrec. 
