In general coax should be better. Toslink has slow transitions that can convert system noise into jitter but doesn't have reflections, doesn't make ground loops and is not sensitive to ambient electrical noise. All comes to jitter that converts to noise. There is no way you can measure anything so the best way is to try. Perhaps you can borrow cables from local stereo store.
OK, so three posters and four answers. Isn't the internet great!
Back of the Oppo unit. I don't see XLR.
As for HDMI, Google tells me inputs are rare on stand-alone DAC's. Essence and NAD M51. What else?
Any other votes for optical vs. coax, assuming modern, highly-engineered, jitter-rejecting DAC?
Just get one of these in the length you need. Better than glass.
If you are really worried about degradation, put a reclocker like the Synchro-Mesh in-line. Then its a don't care. The reclocker will also provide galvanic isolation as well as upsampling to 24/96.
Always use at least 1.25m length for coax: