Literally everything in the audio chain from start to finish colors or distorts the sound in one way or another, no matter how small the effect. Even the cleanest, clearest piece of glass reduces light and clarity by an amount that some may not notice but that can be measured. Now stack more and more of the pieces of glass on top of each other. One of them is the amp and it colored the sound. Doesn't mean it wasn't a quality amp. In fact, some of those most talked about trophies were had at the hand of amps that colored the sound heavily. The name Milbert mean anything to you?
All amps do not sound the same, all head units do not sound the same, all cables do not sound the same (they actually have tests now that reveal why), all opamps do not sound the same, all capacitors do not sound the same, all circuit topologies do not sound the same. But sure enough, people like you who can't hear the differences swear there arent any and come into places like this attempting to force that limitation onto others instead of attempting to teach them that things do sound different and there is a good way to match components in a complimentary fashion.
I have a challenge for you - when you get to know the sound of your new amps and you're satisfied that they're quality (yet sound the same as the amps they replaced because they were quality too and all amps sound the same, thereby making your purchase pointless), upgrade the opamps to some Burson discrete components and swap some stock caps to Black Gates in the signal path. You will hear a difference, I guarantee it. You'd never admit it but that's okay, I'd know you did. But it would probably measure the same before and after the swap. Huh... I wonder how that could be.