I have custom built Odyssey Khartago Extreme monoblocks just because of upgradeitis hit me. Amps amplify sound, they don't sound different. You will be able to play at much louder levels with no distress and have more headroom, however, most people don't listen that loud anyway, so AVR's are more than adequate for most people.
Rated power is not all that is important, people seem to get hung up on that, but I believe they are rated at 200watts each. Memory (capacitance), current delivery, damping factor, DC offset, toroid size, etc. to name a few are every bit as important.
