Well. There are as many opinions as there are people involved. So not having done exhaustive field studies in every aspect of cabling and interconnects I can only offer my person opinion from my personal and professional experience. In other words, my disclaimer is that I can offer you my opinion.
In my opinion:
1. high quality cabling is critical for analog signals.
2. quality cabling is critical for digital I/O only to the point that digital data gets across correctly.
As this answer is somewhat vague and has potential to spawn countless debates I shall leave it that... for now
Yeah, that's a real teaser of an answer
I agree with both of your points. In fact, #2 is common sense for anybody familiar with digital systems.
What I want to get at is what constitutes "high quality cabling"? I cannot think of any reason why something with reasonably high wire gauge, good shielding, quality connectors, and reasonable length (
like these) wouldn't be orders of magnitude beyond the limits of human perception in terms of signal transparency. The monoprice cable I linked has a 16 AWG twisted pair cable with 98% shield coverage and corrosion resistant connectors. And its pretty short. These are all of the electrical characteristics I would expect to make an excellent connector for a voltage bridging connection such as line level audio signals. Yet, folks in the Cables and DBX-free forum call me an a-hole because that cable only cost 7 bucks. Why? What could some esoteric audiophile cable costing $1000/meter improve upon for a line level 10-22kHz bandwidth-limited audio signal?
What about the stock cable on my HD280-pro headphones? It's 3 ft, coiled, stretches up to 10 ft. The connector is gold plated (corrosion resistant). I believe it is a pair of twisted pairs, sheilded. My headphones are nominally 64 Ohm and Tyll measures the headphone response, distortion, and impedance to be
this. The frequency response is rolled off -20dB by 20kHz. The distortion somewhere between 0.1 and 1% from 40Hz -- 6kHz. What possibly could a fancy cable upgrade provide that would be audible? an extra 0.1 dB at 20kHz (which I can't hear over 19kHz anyway)?
If there are some special worst case scenarios where a cable or interconnect can provide an audible difference, I'd really be interested to know what they are, but as it stands, I cannot devise a "killer sample" scenario for any reasonable setup where good quality cables are already in place.
Cheers