Gary, in actuality there's no good reason to "hope" for any difference in sound quality, much less a "marked" one. Your present 645 is conservatively rated, as is the HK practice, and if any difference in the maximum sound level exists with the A23(125 watts)it wouldn't be more than about 1dB. For example, if a brief split-second peak could be played at 105dB with your 645, the A23 might be able to play it at about 106dB, not an appreciable difference. Furthermore, discussion of maximum level capability on brief peaks shouldn't overlook the fact that most of the time the speakers will be using about 1 watt for a comfortably loud listening level, even if a 1000 watt amplifier is connected. You control the amount of power used(with the volume control, of course), not the amplifier.
Your 645 powers the entire 20-20KHz spectrum with level response and inaudibly low noise and distortion. Within its designed power limits you can't do any better than this; there's no mysterious factor that somehow results in better than audibly flawless amplification. This is the case regardless of how expensive the separate amplifier is or how high its maximum power rating is. Don't waste your money.
