Did you ever resolve this, Jayboard? My impression is that it's not like converting unblanced to balanced interconnects because you are taking one standard (S/PDIF, here implemented as coax but it can also be done as Toslink) and converting it to a different standard (AES/EBU). But maybe that doesn't matter.
Unbalanced to balanced adaptor
I'd like to take advantage of the AES/EBU digital input DAC -- just for the additional input. It's a balanced input, but none of my sources is balanced, and the unbalanced inputs of my DAC are already used. Are there cable adaptors that will allow me to take the S/PDIF (RCA coax) output of a transport into the AES/EBU (XLR balanced) input of my DAC?