Ok. I see where I was going wrong with regards to FCP always mixing to stereo. You have to right click on each track and force it to a specific audio output track. By default FCP makes them all 1,2. Same has to then be done on your master sequences.
This still doesn’t help with Soundtrack Pro though. Now I get to export big chunks of audio, one AIFF per track set, but I can’t use Send To Sound Track and then refine dialog clips and so on. Seems like my only option is to open a sequence, Send To Sound Track, make the tweaks and then compile the entire film.
Unless of course someone has a nice trick!
https://twitpic.com/23g5ya