If as Eldartford suggests, Pabelson is correct that science knows but audiophiles don't, then why is there not just one best cable, one best speaker, one best amp.
Because science doesn't tell us that there is only one best anything. Thanks for proving my point about what audiophiles know about science.
For example, the "best" cable, in the technical sense, is the one that distorts the signal the least. (Although some audiophiles may actually prefer a cable that distorts more!) But which cable that is depends on the impedances of the amp and speaker it's connecting. As a practical matter, many cables distort the signal so minutely--a fractional roll-off in the top octave--that the differences aren't audible (assuming you do a meaningful comparison). But when the differences are audible, a few measurements will suffice to explain why.

