Definitely connect the SPDIF out from the Oppo to the Pontus as it’ll sound much better than the Oppo’s analog outs. Don’t discount the importance of the digital cable as it’ll make a big impact on what you ultimately hear. If in budget I’d very highly recommend one of these Acoustic Zen MC2 cables as it did wonders in elevating performance in my digital front end…
https://www.usaudiomart.com/details/649951192-acoustic-zen-mc2-digital-coax-cable-1m/
The DH Labs D750 might also be a good choice although I’ve never heard that one. Incidentally, I added the Iris to get i2S and it was a substantial improvement on many levels, and the AZ cable above provided improvements at that level if that helps give some perspective. Hope this helps, and best of luck.