Ah, I'm assuming you've ABX tested that, castleofargh? Have you heard examples of the silver plated cable being less bright than the copper?
there is no need to blind test that when ohm's law tell us that much. let's take the most obvious hypothetical example for me, 2 cables as identical as can be, in gauge, length, braiding, shielding, etc. but one made of silver and one made of copper. so we can confidently assume that the silver one will at least have lower impedance than the copper one. are we in agreement with that?
now let's plug each cable in turn into, well really most single BA driver IEMs. then we'd measure or sometimes listen to the difference when it's big enough. a BA driver often has its impedance rising massively in the trebles, like these 3 guys:
it's an impedance graph, with an er4sr, an old sony XBA-c10, and I don't remember what I picked for the thrid one(lol, sorry. I just opened randomly some single BA files I have, but all impedance graphs are named "impedance" because I'm a genius, s once open I don't have a clue where I picked it). anyway it's not hard to see a trend in the upper range, based on my own experience this is fairly typical.
now we have basic electricity telling us that for the load(IEM), the source impedance is amplifier output impedance+cable impedance. and that means two things:
1/ if the amp's impedance isn't very small, the difference in cables is not going to matter much when added to the amp.
2/ that the amp+silver cable are going to have lower total impedance.(as we keep the same amp)
now we deduce that the frequency response will be more attenuated in the low and mid range in reaction to the IEM's own impedance response. and when using the copper cable that behavior will be bigger than with the silver cable. meaning that once you match the volume to align at 1khz, the frequency response graph will show a boost in the trebles for the copper cable compared to the FR when using the silver cable. in simple terms, the copper cable would be "brighter" in this example. it's really just good old ohm's law, except that it must be calculated for each frequency as the variables involved keep changing for at least the IEM.
for an example with sources of different impedance changing the FR,
https://www.head-fi.org/threads/feedback-about-gears-stop-doing-it-wrong-impedance.866714/ (self advertising, yeah!!!) I've been told that aside from me whining, the impedance part was easy to understand. or you have the sticky topic about impedance in the main page of the section.
clearly here I'm only paying attention to impedance variations, and FR changing as a result. that doesn't mean it's the only variable capable of affecting the output sound of course. but it's often what's causing the most obvious changes. at least based on my own attempts at measuring stuff when they sounded different to me.
I haven't had a silver cable for years and really don't plan on investing in one anymore, so I can't offer to measure the actual case I was presenting. but I've done a lot of measurements adding resistors of different values between the amp and various IEMs. so I can show some exaggerated examples of how the low impedance "cable"(anything between the amp and the IEM), doesn't always sound "brighter".