I used to think the same for sure. But that is why blind testing isnt always best. An amps use is not always static, and the best setup for one amp is not always the same as another.
They can sound different. And by varying the input voltage from a preamp you can definitely make an amps signature change vs itself. It stands to reason that amps can sound different if you can vary their gain vs input voltage. Different amps mixed in the same setup will cause spl imbalances when input volume is varied. In extreme cases it breaks the experience (think subs and mains at crossover)
You can do this test yourself in your car. Connect your phone to your car stereo. Bluetooth or wired (doesnt matter). Listen to a song loudly with sharp deep impulses. I suggest Phil Collins “I dont care anymore”. Now turn your phone volume down and car stereo up to match volume. Now turn your phone volume up and car stereo down to match volume. Report back…..
This is exactly why calibration is needed when setting up subs properly. You can do the same test as above by changing the sub gain vs AVR output trim. There you go.
