Alright, this is the small, insignificant hill I'm prepared to die on.

Firstly, placebo is the wrong word - I'd argue it's more of a perceptual phenomenon.

Why? Because we prioritise visual information over auditory information - we know this from the Mcgurk effect where hearing a word said over a video of a different word being said causes people to hear a different (third) word.

In this scenario all the ABX studies would show this had no effect on the audio, but we can clearly see from studies ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3196040/ ) that what is perceived by people and what auditory information they are receiving can be different things.

This would mean that we could equate the ABX studies to be victims of looking for or measuring the wrong thing. The see visual information on the cables as a confounding variable, when in reality they should be considered as part of the dependent variable - with audio and visual data being seen as one/a whole.

Also, we know that 2 headphones can have the same/similar FR, but will/can sound different.

So, what we need is a blind or some kinds of ABX test where copper cables are put in either copper or silver sleeves and vice versa, not tell the participants and then see what the results are. I haven't been able to find any studies on this, and until I do I won't accept that cables don't change a persons perception of how music sounds - and after all, perception is reality.

Amazing--you can still sell a 2000 dollar amp that nobody could tell the difference between it and my relatively cheap FiiO 7. No noise, plenty of volume--NO PROBLEM.

I feel like people always feel attacked when you point out that a difference probably isn’t real. But I think we need to stop saying you don’t hear it. Human hearing is clearly not merely the process of tranducing sound pressure. You cannot separate objective “sound pressure at the ear drum over time” from whatever other post-processing happens in your brain, and the latter has been repeatedly established to be a significant factor, which you can test for yourself easily enough if you doubt it. This makes it easy to make the attribution error that something is producing a different sound wave, rather than merely changing the cognitive aspect of “hearing”.

It's supposed to be quite a debate over wire qualities, and a large amount of hotheads out there think they can just identify some $2000 dac from some $1000 dac or something. Yes, there have been scientific studies to test these theories and sadly, those hotheads make it seem as if the audiophile community is in words, "obsolete". There is a fine line though. After working for years with music, perhaps if you're a producer or a good sound engineer, there are those out there who can tell differences between lots of things in terms of audio. But if you're just sitting in your bedroom listening to music and suddenly decide your want a $2000 dac/amp, you won't be able to tell the difference. Another thing, if you do tend to work with music throughout your life, then I guess your subconscious begins to identify these small differences, because it can. But it's correctly said that lots of people do automatically defend something which they believe they support. Sometimes myths are made because the wrong people represent certain things.

I get custom cables made so I can have the length & color & termination I want do thay dramatically sound better no but it isn't any worst

There is a long list of studies, experiments, and blind tests here. One of the best lists I’ve found.

https://www.head-fi.org/threads/testing-audiophile-claims-and-myths.486598/

The key takeaway after a meta review of all them is …

“The clear conclusion is that ABX testing does not back up many audiophile claims ... Any change in sound quality comes from the listeners mind and interaction between their senses. What is claimed to be audible is not reliably so.”