Are there differing qualities of optical cable?

It shouldn't sound different unless the DAC is not handling jitter very well in which case you may need to experiment to find out what works best in your situation.

I assume you are playing CDs which should be fine. Just avoid using this DAC for any higher than 18 bit files as it probably just truncates and throws out the least significant bits on any digital music above 18 bit.

Since the consensus seems to be that coax is better than optical, I ordered the DH Labs D-750 coax cable.
Hopefully it will do an even better job than my Monster optical cable, which is sounding quite good right now.

The Oppo does use a switching power supply for the digital board. Some of this switching noise could be making it into that COAX (if you are using the Oppo as a Transport). The toslink fiber cable electrically disconnects the DAC from the transport, so it could be insulating your Gungir DAC from that switching power supply noise. Just a theory.

rvpiano
My question is, are there different qualities of optical cable you can use, or is one the same as the other?

Yes the polished optical glass cable is the best (can’t bend it too much), Wadia had these as an ST type connection with an AT&T reciever (not Toslink), with a small smear of what called "optical indexing fluid" on the ends and then plugged in. The fluid was very expensive and optically clear, it gave a far better coupling between the end of the glass fibre and the receiver lens. Would work with Toslink as well I would think.
https://www.newport.com/f/index-matching-fluid

https://www.ebay.com.au/sch/i.html?_odkw=ST+optical&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.XST+optical+cable.TRS0&_nkw=ST+optical+cable&_sacat=0

Cheers George

I installed a new glass fiber optical cable.  It was a definite improvement over my previous Monster optical.
Today I just got a new DH Labs Silver Sonic coax cable.
Again, a definite improvement over my previous Cardas coax AND definitely better than the new optical.
So, double improvement!
Thanks for all the suggestions.

Question:  Does coax cable require burn in?
It sounds great right now.