No, they do not all sound the same under different loads, and its fanciful to expect that they would and will. Amplifiers are tested with resistive loads, and is therefore limited in telling you how it will drive a given loudspeaker. Very few amp manufacturers actually test their amps under varying condition of load. This was another point that Peter Walker made continuously. For one thing source impedance varies from amp to amp, and those with a higher source impedance will sound more different under varying loads than one that has a very low source impedance. That is one reason that I am keen on Quad amps, as they have a very low source impedance. \n\nIn comparison to this issue, measuring amps for minute levels of distortion connected to a resistor gives very limited information. That is what you would expect the way impedance curves look and then even more to the point look at phase angles. When these get to negative 45 then there are huge differences in true and apparent shifts resulting in large current fluxes. To think that all amps will act similarly to these situations is absurd in the extreme. So no all amps do not sound the same. Not by a long shot.\n\n\nDo you agree that two amps that measure the same should sound the same? Or whatever audible differences claimed between amps should be measurable?