The amps I am using are the Mcintosh mc611 600 W mono blocks.
When listening to music there are peaks and valleys and dynamics, I have always used the Rocky Mountains versus Appalachian mountains when comparing Sonic detail. A more powerful amplifier I believe tends to ascend to the peaks more effortlessly to better represent the accuracy of a Real performance.
The tonality of an amplifier is of interest and maybe higher quality amplifiers achieve this in a more impressive way; also the handling more complicated material such as Home theater stuff and classical music.