Did you check the V3 manual on the Grace website Support page?
The V3 is set up to transmit digital signals from three different outputs:
Coax (75 ohm)
XLR1 (110 ohm) - labelled as AES1 in the V3 manual
XLR2 (110 ohm) - labelled as AES2 in the V3 manual
Coax and XLR1 share the same transmitter capable of either AES/EBU or S/PDIF, selected by internal jumper
XLR2 has its own transmitter which always transmits AES/EBU.
I think what you want to do is use XLR1 to send a S/PDIF signal. No problem. Set the internal jumper to S/PDIF (see the manual for the jumper, I think it's labelled "consumer"). If you're to use XLR1 to send S/PDIF over an XLR > coax cable, you technically should use a 110 > 75 ohm impedance transformer.
That said, I don't use one and it seems to work just fine for me. I run S/PDIF XLR1 > coax for my DAT, and use the coax S/PDIF output for patchers (of which I rarely have any, it seems).