There is no way all amplifiers sound the same. There are different set gain settings, output power and distortioin levels. Pre-amplifiers are even more reaveling, and DAC being the most important component of all.
Anyway, all amps are same and sound the same is a false. The other day I watched a youtube video of two different speakers with different separtes playing music. Through my own speakers, one sounded dull and distorted, while the other, my own little computer speakers were putting out "life" like hifi sound.
I guess this means the signal is very important, therefore I think the DAC is the most important, and the preamp which stregntghens the signals, and amps last. But noethless, amps are important because they can add color to the sound. I guess the best gear for me are the seperates and speakers that play the source and stay original to the content.
But the more neutral and transperent one wants, the more expensive the combo is.