Which is better Coax or Optical cables

@thankful If this is your setup as you listed it:

Oppo 105D
Primaluna Dialogue Premium Integrated
Emerald Physics KC II Pro speakers

I don’t see how you would need a digital cable at all, your integrated doesn’t have a built in Dac nor do you mention an external  Dac. So you just need analog RCA cables to hook your Oppo up to your Primaluna.

As @kijanki already pointed out, it's system dependent. One benefit of optical is the inherent electrical isolation. Lifatec makes excellent glass cables capable of handling 24/192 files.

http://www.lifatec.com/toslink2.html

"But" if a person were to place a DAC between the Oppo and integrated there would be a need one.

""But" if a person were to place a DAC between the Oppo and integrated there would be a need one."

True, however it’s not as simple as adding the DAC and cable. More often than not it becomes an exploration to find the right combination that compliments your system. Have you considered other paths for upgrade?

Given that the contrasts between cable types has been addressed, and that you currently own only a 105D, the question becomes: Are you considering the purchase of a DAC and for what reason?