Danlib hit the nail on the head. Two amplifiers can measure nearly identically in all of the usual tests and yet sound significantly different. Why? Because amps are filled with passive parts like resistors and capacitors and wire that all sound different even when rated at the same value.
Anyone who has actually listened to different brands of resistors or capacitors of the exact same value knows this. I believe dialectrics have a noticable effect on sound and they are everywhere including the circuit boards.
Even the solder used can affect sound quality. Recently a popular high end manufacturer changed to lead free solder and all of their gear actually started to sound different (in this case better, thankfully).
Anyone who has actually listened to different brands of resistors or capacitors of the exact same value knows this. I believe dialectrics have a noticable effect on sound and they are everywhere including the circuit boards.
Even the solder used can affect sound quality. Recently a popular high end manufacturer changed to lead free solder and all of their gear actually started to sound different (in this case better, thankfully).