Your further inquiry about blind AB test is a bit odd to me. Like if I was in a restaurant, complaining to the waiter that the dish wasn’t satisfying and the cook didn’t do a good job. Then the waiter would ask me if I blind AB tested the meal with spice matching against another restaurant? If that would happen I would laugh at him, then saying: „wait, are you serious? - let me even laugh harder.“
I agree that a proper designed amp is neutral, adding nothing to the sound nor emphasizing certain frequencies. But then still, some manufacturers seem to have a signature sound to their brand/products.
The problem isn’t distortion either, maybe the variance in loudspeaker impedance through different frequency bands and that interaction with the amps output stage resulting in a rather analytical, cool sound.
My main complaint was about, when SMSL is adding DSP functions to allow customers altering the sound to their tastes, why only in the highs and the lows disregarding the mids (because there is the most need of action according to my opinion)?