Should I connect my OPPO BDP 105 to my PontisII?

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://tmraudio.com/hidden-parent/fresh-arrivals/acoustic-zen-mc2-digital-rca-to-bnc-digital-coaxial-cable-mc-2-single-1m-interconnect/

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.

Which one if I may ask?

What output are you using from the Oppo?  The HDMI output is for A/V only and doesn’t work for i2S if that’s what you’re using. 

Well, first I wouldn’t use an optical cable for to the Pontus as you’re introducing additional conversions to and from light transmission and it’s limited to 24/96.  Check the settings in the Oppo to make sure the digital outs are active and properly configured, and you also may want to try a 1m wire SPDIF digital cable in case the optical connection on either side is compromised (a regular analog RCA interconnect may work for this too just for trial purposes).  Here’s a decent cable that’s not too pricey if you need one, and you can easily return it if it doesn’t work…

https://www.amazon.com/Geistnotes-Apogee-Wyde-Cable-WE-RR/dp/B01N29180M/ref=sr_1_1?crid=RBCMHOO0RK3W&dib=eyJ2IjoiMSJ9.BaI3PBEjKIocRjAsFYUFL87J2dPa9D_7Bf5HPi1GRxuXOcDjEvJtFBXBwae46wQS.XdUyeEpPfIdiQ-3B13GSh513lUYCIQoL1kJuoYG4md4&dib_tag=se&keywords=apogee%2Bwyde%2Beye%2Bcable&qid=1712844475&sprefix=Apogee%2Bwyde%2Caps%2C147&sr=8-1&th=1

Good luck!