Why do digital cables sound different?

Did you test only by doing a rapid A/B between cables? In my experience, that methodology usually yields a "no difference" conclusion.

I love threads that last 7 years!

Osgorth, I think you've just done the test many here may have preferred you hadn't. Well done! From a technical point of view, there's no reason for digital cables to sound different provided they're made to a good basic standard, but there are plenty of audiophiles with bat ears who can 'hear' some amazing differences in various cables. I'm not surprized at your findings at all.

As for Drubin's comment about A/B comparisons; I've written in previous threads that this is the ONLY way to truly listen for discrete differences, as it allows the brain to do a true real-time comparison.

Long listening tests (where you listen for a longer period), then change cables and listen again requires you to compare the new sound to your memory of the first, which is less accurate IMHO. Not only are you relying on your memory of the sound, but you can introduce variations due to shut-down and restart of components, unlplugging and reconnecting cables and so on. Such comparisons work for hearing gross changes, but not the very small variations in digital cable sound.

Allow me to defend my position with this observation from personal experience: switching between tape and monitor when dubbing to a cassette deck, one might be hard-pressed to hear much difference. One would be very wrong.

Playing around with these in various configs and switching inputs back and forth (both blind and active, I used some fellow audiophile friends) - there is NO difference whatsoever between ANY of these cables.

This matches my experience. I maintain that properly engineered and matched equipment should not give a hoot about cabling - as long as it is adequate and you don't have a ground loop, RF/EM problem or contact problem. I suspect that the great differences reported stem from running equipment at the limits of its ability - amps that are already clipping and loads that are mismatched to begin with....situations where the slightest difference might influence the sound enough to be audible. Just two cents...and I admit I could be completely wrong.