Best interconnects & speaker cable? I don't get it

I don't know if there is a question here but I'm posting this to see if there is something I'm missing or overlooking in this observation. To the point, I've read many posts arguing the benefits of one or more conductors over others and I almost understand some discussions regarding, at least, comparisons of wire gauge for speakers. Maybe it relates to my less than well developed ability to discern subtlities in sound quality but I really can't hear much, if any, difference between interconnects or speaker cables.

As an example, I was recently experimenting with an amplifier selector (Niles DPS-1) which can accommodate a max of 14AWG speaker wire. In doing so I had to disconnect my existing cables which are "high end" 12 gauge per leg bi-wires. In making this comment I realize that just because my old wires are big and expensive does not necessarily mean they are the best match for my system or even any good. But...even though I think I am able to hear some small difference between them, to say that I think one is better than the other would be a stretch.

It seems to me that there are factors that would logically lend to the issue of quality, the primary of which would be conductor resistance and/or impedance. However, for transmission of line level signals, I can't see impedance as a significant factor.

All that being said, I believe that some listeners with acutely honed abilities can actually hear these differences and, in a way, I am somewhat glad that I don't; It makes wire choices much easier and way less expensive.

My current system consists of Shanling S-100 CD player, CALSigma 2 DAC, Rogue Audio Sphinx and Martin Logan Odyssey speakers with various interconnect and speaker wires.