I think the 9 pin sync is for connecting multiple adats together so they work as one (as far as adats could ever work as one) and in your case should be ignored, no audio is transferred. The optical connectors are what you need for 8 audio I/O
Yep it´s for syncing several ADAT units.
EDIT: Of course that Split guy again…
I think the sync of the 9pin dat is proprietary, ie you cannot derive a wordclock from it.
If locking two computers together it would be best to use the wordclock from the master comp soundcard to lock the slaves soundcard to and then use MIDI timecode via a midi cable to provide a timebase for the slave computers sequencer.
Just remember if using digital audio you will need to clock one of the card from the other (best with word clock imo) otherwise you may get the odd click as the two soundcards clocks drift)
No, I think the optical does contain clock, but IMO it’s better to use the separate wordclock.
Don’t see why one optical cable is any different from another, particularly over a short run. as long as the end bits fit