This really does not answer your question, but I though I would mention that I untill recently I was using a MOTU PCI 424 card allong with my Decklink HD PCI-X card. When I went to do a project in HD, the Decklink card would not work propperly because the MOTU card was on the same bus and was clocking down the Decklink card too slow for HD. Since I also had an ATTO card which needed a fast bus, the MOTU card had to be sacrificed.
I would think that decklink’s RS 422 interface could be accessed by Pro Tools for syncronizing to a tape source but not sure how.
bk