I have said it a million times: RC's amp doesn't prove that every single amplifier sounds the same out of the box. It proves that the differences are due to real physically verifiable phenomenon and not some voodoo that comes with the name on the amp. Once these differences are accounted for (as RC does in his tests), then the amplifiers will sound the same (ignoring the flawed human perception of sound).
Because we all know amps are the number one cause of bad SQ...enclosures, room acoustics, speakers, headunits and sources have pretty much nothing to do with it...when was the last time you literally swapped an amp out, giving your subs the exact same amount of unclipped power in the exact same enclosure, and honestly thought "wow this sounds incredible compared to that old piece of crap"