The $25 Lepai LP2020+ integrated stereo amplifier plays exactly the same notes as a $42,000 D'Agostino Momentum amplifier. Exactly. The rhythms, melodies, and harmonies are all the same. Granted, the Momentum is considerably more powerful, so it can play louder, the bass will be more potent, the treble is clearer, and the stereo sound stage takes on an almost three-dimensional quality, but the notes, they're no different.
For me, the real difference between the two amps is how they translate music into sound. The emotional connection to the music is stronger through the D'Agostino Momentum; it's a giant step closer to hearing all of the energy/passion the musicians were putting into the music when they recorded it.
It's akin to the difference between what a great chef can do with ingredients that the average person could never come close to matching. The "notes" may be the same, but flavors are a very different story. With amps, the sound, as opposed to notes, is the first thing to go. A great amp strips away the artifice of sound reproduction and lets more of the music shine through.
Vacuum tube amplifiers measure and sound different, some say better, some say worse than solid-state amps, but again they both play the same notes. There are those folks who believe the only scientific way to settle this debate is to "blind test" listeners to "see" if they can hear the difference. That's cool, if that's what you want to do. Prove that all amps sound the same, and then buy the Lepai LP2020A+ and live happily ever after. Me, I'll stick with my Pass Labs XA100.5 amps, and live happily ever after.