wrote ...
Now to partly answer my own question, I came across
a great website that discusses the issues I'm pondering.
He titles the articles "Skin effect" but in fact spends very
little time on true skin effect.
http://www.st-andrews.ac.uk/~www_pa/...io/Analog.html
He does provide many graphs showing very clear effects
of different cable construction--all at about 100kHz, and
most less than 0.1dB-- but measurable and predictable,
nonetheless.

But NOT audible. This is the kind of "pathological" wacko
"pseudo-science" that people get hung up with when trying
to avoid the real world (for whatever reason?) The website
appears to do a good job of explaining the physics, but it
doesn't follow through with what effect (or not) you will
actually HEAR at audio frequencies.

"You should also understand how the Skin Effect can cause
problems with wideband signals..." But no explanation (that
I saw) AUDIO (20Hz...20KHz) is NOT "wideband".

If you really want to discuss "skin effect" at 20KHz and
"audio harmonics" above 20KHz, you should probably
go and find one of the "golden-ears" high-end audio forums.
I would wager that only a small fraction of people on THIS
newsgroup can hear to anywhere near 20KHz. (Likely the
same on the "golden-ears" newsgroups, but they won't
admit it! :-)