I don't know.But I do know that in order to record anything,the VS needs some type of clock,either it's own internal one,or one coming from Digin 1 or Digin 2.My understanding was that you wanted the 2 machines to be in sync when doing the 2 track ,and in this scenario one would have to be master and the other slave.But it might work,give it a try,you won't damage anything by trying.I have one VS-990EX and I HAVE tried this:when all my tracks are full I send them out via S/PDIF to my Tascam CDRW-700 CD burner and record them to a CDRW,I then reset the clock on the VS to DIGIN 2(optical) and record the CD back into the VS on 2 Virtual Tracks.Now these are not in sync with the opriginal VS tracks but I don't care 'cause I can now continue recording on the other empty Virtual Tracks to embellish the 2 tracks from the CD so I end up with potentially more than 16 tracks although I've never yet needed to go that far.Sorry for the typos.