I am interested in my amps power rating because in order to accurately reproduce the dynamics of music you need hundreds of watts, even with a high sensitivity loudspeaker. I know my speakers have low sensitivity, if i could afford a 1000W amp i'd love one. But i'll have to do with 220W right now. As for output impedance this is useful for telling you how much control said amp will have over your loudspeakers (damping factor). I also like to know as much as possible about speakers because if you know their frequency response (waterfall plot), then you know what they are accurately replaying and what they aren't. I hate bright speakers, and a waterfall plot can tell you this before you even listen. These are just some of the things i like to know. I'm also interested in toroid rating, smoothing capacitor ratings, everything. I'm a technically minded guy with a degree in physics, i like to learn how everything works - not just hifi. But i also appreciate that most people are happy to just sit back and listen, in many ways this is better than my aproach because i sometimes worry to much about setting things up right and figures that i forget i'm suppoesed to be enjoying the music. My curse i guess