Without a blind test, I don't doubt you do think you hear differences. You seem to be convinced that you should be able to. But the truth is, that all properly designed solid state amps are calibrated to sound exactly the same... Sony, Marantz, Yamaha, McIntosh... It doesn't matter. They all have stone flat response with no audible distortion. Expensive ones and cheap ones, the only difference between them is power.
I've had several amps over the years. When one burned out and was replaced, all my EQ settings remained the same. I've done quite a bit of careful line level matched A/B comparisons between CD players, SACD players and iPods. Those all sound the same too.
Now you might say, "If everything sounds the same, why would anyone spend thousands of dollars on high end players and boutique amps?" That question, I don't have an answer for. I can only speculate that they haven't gone to the trouble of controlled comparison testing to find out for themselves.