I did not look at the videos.
10 m of 12 AWG copper wire is about 50 m-ohms, so 100 m-ohms or 0.1 ohms for a speaker cable (two wires, + and -) ref
https://en.wikipedia.org/wiki/American_wire_gauge Compared to no wire (direct to amp) using an 8-ohm speaker, the difference would be about 0.1 dB, right around the audible threshold of detection. It would be around 0.2 dB for 4-ohm speakers. So a good DBT should be able to detect the difference if you add 10 m of cable. In the real world you increase the volume 0.1 dB to compensate. The difference would be higher with smaller wire, of course.
Between silver and copper, I call B.S. Silver is a
hair more conductive (~5% IIRC) but at that point it is a germ on a flea, not really relevant. And would not significantly affect the frequency response compared to copper. I have read copper is "warmer" and silver "colder" for decades and am convinced it is people hearing with their eyes.
IME/IMO - Don