Matt --

I wouldn't worry about ground loops on a digital signal. There should be sufficient noise immunity so that the data integrity is maintained. The noise would need to be sufficiently bad so that it cause your digital input to make decoding mistakes (bit errors). This is not very likely since you are probably running a relatively short piece of cable between your gear and my guess is that all of your gear is plugged into the same power strip or outlet. If this is the case, your grounds are probably all OK.

There are some who will claim that the coaxial input is better because the optical cables tend to introduce more "Jitter". I have never heard (or had anyone successfully demonstrate) this phenomenon myself.

Dave