^I agree to a point, the mind only remembers difference in sound over maybe a period of 20 minutes or so, but I spend a lot of time in my vehicle (in sales on the road 8 to 10 hrs a day) I get to listen to my gear for a pretty good period of time and I can usually tell what's good or not so good or what's pleasing to my ears.

And easy way to test for difference in sounds from different amplifiers is to visit a high end home theater shop (no best buy) they can easily switch from amp to amp and use the same source same speakers...this is why I have an arcam receiver right now...huge sound difference over everyday brands.

Higher end brands spend more more on internal components/power supplies...the end result is better sound, that's a fact...problem is "how much more money are you willing to spend?" to see a result in better performance