I'm not sure there is a debate here.
Yes, but if the tube amp has top quality output transformers the impedance shouldn't be an issue. In my experience with high quality tube amps the differences between SS and tube are quite subtle. Vintage Macs and others tend to have rolled off tops and fat and lose bottom ends due to their design and possibly their transformers. OTL designs definitely sound "different".
Perhaps, but since both were designed to work with low impedance loudspeakers, I believe Mr. Hirsch was of the belief that the operating principle of the amplifier was not relevant to the sound quality as long as both measured reasonably well. While he did measure 0.000000000000X IM, THD, TIM etc., he also said that these numbers were not really relevant past a certain point.
"Useless" may be a bit strong, but I agree.
Cheap transformers will certainly have that effect. I am not familiar with the devices under test here, but if the tube amp is using economy or some vintage transformers that would certainly alter the sound in a manner described by the listeners. I had assumed the comparison was using top flight amps operating to a spec of +/- 0.25dB 20Hz to 20KHz or thereabouts.
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