“the current audio device does not support the number of outputs set in the sequence settings audio outputs tab”
that’s just about the monitoring, it wont affect the exporting.
you get an option to down mix to stereo, that’s good.
again, that’s just about monitoring, not exporting
“my file has 6 tracks but 4 of them are blank”
your sequence may still be set to stereo.
compressor is getting a stereo signal from FCP, and just ads 4 blank tracks
“I want to export the file with the same 6 tracks embedded + untouched”
this is how I have been doing it.
hopefully Michael Gissing will also chime in.
in FCP, open your sequence’s settings, go to the Audio Outputs tab.
select 6 outputs.
set all 3 pairs to Dual Mono,
and set all to zero db.
back in the timeline, right click on or near the lock icon, for each track
and choose an output.
track 1 goes to 1, tack 2 to 2, etc.
make sure the audio clips are volume and pan neutral:
select it al, Option Command V to remove attributes pan and volume that you may have added.
i have been doing it this way to deliver files for a DCP.
(I have been exporting the audio separately)
when we tried to play the file in a theatre, the audio system didn’t recognise the tracks,
but we were able to fix that in Quicktime Player 7 (you should have that)
by opening the Properties window,
choosing Sound Tracks > Audio Settings,
and adjusting the track assignment
nick