Thanks for the advice, Loren. I have a number of firewire cables hanging around so I tested them all. Unfortunately, no change with any of them. In my forum searches, I have heard of grounding problems with various audio interfaces and had a feeling that might be the case.
I also ran into some instructions on defeating the ground to solve the problem, but I'm interested in opening the box to do such a thing. Ground wires are there for a reason.
Black, I have found others who have the same problem (the squealing noise) so I'm not alone. It seems to be a rare occurrence though.
Who knows... maybe it's just a lemon? At this point, I really don't care. I'm just mad at this box, and I'm done trying to get it work properly. I didn't pay anything for it (it was purchased for me), and I know someone else who could use it, despite its faults. So I don't see it as a loss.
For anyone curious, I'll send an update once I purchase and test the Edirol. Fingers crossed everything works out.
Thanks again everyone for your help and advice.