You just put only those two channels into the mix. Pan 5 hard left, 6 hard right, both at 100%, the other channels at 0%. I can show you how to do it.
You'll also need to check that the stereo channel mix level is also set to 100%, in addition to ch's 5 & 6. But you’ll want all other channels set to 0%, unless you want them mixed into the S/PDIF out stream as well.
Can you do that if you have the mix set to DIN to have 7/8 digi stereo track??
According to the block diagram in the manual:
While in multi-track recording mode, the S/PDIF output is always connected directly to the stereo mix bus.
The ST REC switch routes the S/PDIF input either directly to the SD card (DIN) or to the stereo mix bus. So it appears one can mix all six analog inputs and the S/PDIF input to the stereo bus if desired.
DIN REC MONITOR switches the headphone output between the S/PDIF input or the mix bus. It doesn’t appear to touch the S/PDIF output.
If you have the stereo record to DIN, the digital input will record to the "stereo mix" which is track 7/8 correct?
Correct