Are there differing qualities of optical cable?

First, about methodology. Yes, a modern audioanalyzer like a DScope or Audio Precision is indeeed more discerning than even the best human hearing. They can measure subtleties that no human can hear because they are beyond the threshold of human hearing acuity. Think of the parallel with microscopes or telescopes.
As for interfaces and cables, this discussion was about the cables, not the respective merits of the interfaces. If you compare digital interfaces, usb is best for jitter, distortion and noise, followed by coaxial and just after that optical. Do these differences matter? I doubt it, as they are at such elevated levels that no human is likely to hear them (under controlled conditions, of course).

@willemj

The interface is indeed the issue and it depends on the methodology of implementation.

I would argue that USB digital has been a disaster for many years.

Even today day I think the approach can be worse than Coax or Toslink because of logic induced modulation noise induced back into the power supply of the USB DAC.

Does it matter - absolutely! Non random Jitter is quite audible even at picosecond levels. Check out Cranesong website for some jitter demonstrations.

Willemj:

So you evidently believe that the differences I, and others hear, is imaginary.
The objective listening of listeners to various cables is real.
Obviously the testing instruments are not capable of picking up the kinds of differences people hear.
These tests are useless and hence, worthless!

Blind faith in current scientific methodology leaves no room for discovery.

Blind faith in current scientific methodology leaves no room for discovery.

And Blind Faith Live in Hyde Park June 7, 1969 SBD London, England is definitely worth listening too :)