I was at a seminar once, professional audio systems, hosted by Sennheiser, and they were explaining with demonstrations the differences between certain audio products. We had two different sound systems on show, next to each other, and one was BIG, while the other used a vertical column of very small speakers on a sub unit. They demo'd the small system - it was good, very good in fact. Then he went behind, pulled the plugs out of the CD player and swapped them. He stuck in a CD - Dire straits, I seem to remember - Money for Nothing. Turned up the volume and we heard the 'big' system. We then stopped and he asked us for single word comments on the difference. He then spun the BIG system around on it's wheels and there were no cables plugged in! All he had done was unplug the CD player and plug it back in. The source material did the rest - we all KNEW we were listening to the big system, not the tiny little speakers in the thin columns. Brain and memory worked together to convince all of us. Psycho-acoustics.
If you spent hundreds of pounds/dollars on something that takes at least a minute to wire in, your brain simply will not let you not hear a difference. I don't see the people who can hear what I can't as liars - I know my hearing is now gone higher than 16KHz, but 16-20KHz is a tiny difference on a piano keyboard, and I can still tell when material is lacking in HF sparkle. What I cannot accept are hi-fi 'staple favourites' that wave in the face of physics, or worse, bastardise physics by twisting it with a tiny dollop of physics and lots of surrounding rubbish.
Directional cables, and special cables that carry the audio on the outside of the cable - that one always makes me smile. It's true - but only at microwave frequencies.
The notion that you can hear a switch in the circuit just makes me smile. What properties could a switch actually have? Resistance. Possibly capacitance if the switching blades were very close together? Inductance - I can't see this one? What other property could have an impact?