Try the Bose community?
LOL This is the Bose community, just most of us changed 35 + years ago. They are still in the shop somewhere under silks, along with 20 + other pairs of retired, or in the process of being made speakers..:-)
OP it is "OUT IN, OUT IN. Out of the tape monitor into the EQ, out of the EQ and into Tape 1 or 2. Select the tape loop your going to monitor (1 or 2) and make sure your plugged in there. 1 or 2 (if you have two) And engage the monitor switch or button. Actual pre in or out is not the best way, that is NOT passive, it is in the path and active.
The cables, the wire inside and components were just CHEAP...
It's better to use tone control and see if the "LOOP" is better or worse. In the preamp path you can't disengage the EQ.. Your stuck with CRAP.. OK...