I did reference the Carver Stereophile challenge - where a $600 Carver amp is nulled by Bob Carver (with RadioShack parts overnite in his hotel room) against a "five figure tube amp"
after adjusting frequency response and output impedance to match, Stereophile's "Golden Ears" couldn't tell the difference in blind listening
so the literal "all amps sound the same" is a strawman - amps can differ in frequency response and output damping by enough to be audibly distinguished under DBT conditions
but as a understood and controllable difference it is "uninteresting" in an engineering sense - it means designers just build in EQ to give their amps unique "voices" - not that there is some mysterious superiority of audiophile tweaks, parts or tubes vs SS in amplifiers