Connect new powerbook with UA-3?, Help! can't get it to work Options

Anyone have advice on connecting an Edirol UA-3 with a new Powerbook running OS 10.1.4?

I just purchased the UA-3, and cannot get the digital connection to function no matter what I do. I already returned one unit, after speaking to Edirol tech support and deciding together that it was defective. Now that the second one does the same thing, I'm beginning to wonder....

I'm trying to import recordings (my own) from a Sony DAT to the powerbook, using the S/PDIF line and a propietary sony cable. I know that the signal is leaving the DAT, because I have connected it to the optical IN of a minidisc player and it sounds fine. As far as I can tell, all the settings and switches are in the right place, and the sample rates are the same (i.e. 44.1. Setting it to 48 doesn't change things). The analog line does in fact work, and aside from some weird beeping in the first few seconds of the first recording, it sounds decent. But that defeats the whole purpose of getting the UA-3, which was to stay in the digital domain from DAT to CD.

Other fun symptoms:
-- occasionally the UA-3 output does pick up something of the digital signal, but it sounds fuzzy and distant.
-- occasionally horrible buzzes come out of the mac sound system.

So - do I have to conclude that the two machines just don't work together, or does anyone have an idea what might be wrong? (would the UA-1D work?).

Any help much appreciated,
d. noveck