I don’t think all amps sound the same, but usually when I hear about reviewers hearing "things I never heard before" it speaks to the device exaggerating one tonal range over another. Especially true with speaker reviews. This is a never ending cycle, of chasing more details and more things you never heard before, sometimes leading to a particular sound that is so far from neutral it’s hard to hear. Sometimes that is good for listeners who prefer lower volumes.
My point is, be careful chasing details. In terms of speakers that sound remarkably better, D’Agostino, Vandersteen (yes, they make amps) and Luxman are among my favorites. All have glass smooth mid to treble, liquid like midranges and great bass.
From my very poor and now dusty memory, Coda had extension but never had that relaxed feeling of the others or a great tube amp. My memory now is hazy and I encourage listening.