Originally Posted by Howie J
The optical input on a 002/003 is not the S/PDIF input. They are the ADAT 1-8 inputs. The S/PDIF ins are RCA jacks on the 00X series. Set your input to an ADAT input and it might work then.
Just out of curiosity...why are you looping audio out of the MacPro back into it??
The optical input on the 003 is indeed spdif if you set the spdif in to optical in the hardware settings. I use it that way all the time.