Dumbeat, in my experience cabling can make an audible difference which does not show up in the kind if measurements you are asking for.
Since I'm a speaker guy, I tend to give a lot of credit and/or blame to the speakers. I do not look to cabling to fix my speakers, nor do I blame the cabling if my speakers suck.
At a recent audio show we exhibited speakers that have a secondary array of drivers, firing to the rear, which are not very loud relative to the main speakers. Their calculated contribution to the summed SPL is only about two-tenths of a decibel. This secondary array of drivers was connected to the amplifier by a separate speaker cable from the main array. This last detail is important to what I'm going to describe.
During set-up at first we hooked everything up with cabling that we had on hand. Then several hours later the cable company we were sharing the room with arrived (Clarity Cables). We changed cables one-by-one, because we had time, and because we wanted to listen for changes and decide whether the original cabling or the cable company's cabling sounded the best. No one from the cable company was present for this.
I'll only describe what happened when we changed the speaker cables going to that array of rear-firing drivers, the ones contributing only .2 dB.
When we made that change, a harshness that I had been blaming on my speakers disappeared. I had been planning to make a crossover change before the show opened the next day, and with the new speaker cables going to that rear-firing array, it was clear that no crossover change was needed. I was amazed and relieved.
The amplifier designer (Hans Looman of Resonessence) is the one who explained what was going on. His explanation shifted my paradigm about cables. He said that the original cables had been acting like antennas and picking up radio frequency signals, which the amplifier's feedback/error correction circuitry interpreted as distortion. The error correction circuitry was therefore working like mad trying to correct this "distortion", and THAT was the source of the harshness I had been hearing. It was coming from the amps, as they tried to correct for something their error-correction circuitry interpreted as a distortion. The Clarity Cables did not behave as antennas and so the amplifier was no longer trying to correct for the radio-frequency "distortion".
Given that the secondary array of drivers was only contributing .2 dB, it would be unlikely that any minor changes in their frequency response due to the cabling change would be audible. However if that cabling change made a significant difference in the amplifier's behavior, that difference would also show up in the main speakers, where it could theoretically be audible (and in this case, it was).
I think this is an example of a non-obvious mechanism by which cabling can make a difference. And no I don't have data to prove this, so you'll have to decide whether what I've described passes your "reasonableness" test. Truth precedes observation, and observation precedes data.
Duke
