IanG-UK has put it very nicely in the above post. I do think that we should all be very critical when spending our money in this hobby. Too much of snake oil out there. As for the Ethernet cables I believe the difference we hear has to do with jitter reduction due to EMI/RFI rejection. Here is a good article that hopefully explains the point more clearly:
https://darko.audio/2014/12/global-feedb...ifference/
https://darko.audio/2014/12/global-feedb...ifference/