I think you are correct, and I say "I think" cause I was wondering the same thing and as you said, the manual won't explain it right, anyway, I own a atb32 and mostly for mixing as well, so what I discovered is that the submaster section is like pre asigned to the stereo out, there is no "asign to L and R button, and using the monitor subgroups inputs will cut the signal from the subgroups to the main out if you push the tape button on the subs master section
and you have to turn the pot's on the submaster section in order for them to listen to the subgroups therefore to send them to the main out and monitor out
I hope I am making any sense, English is not exactly great on me....
