OK, I just skimmed the entire thread, and did not see the following mentioned anywhere:
Look at Figure 8 here. This is a typical distortion characteristic for a class AB amplifier. This happens to be a brute, an Adcom GFA-565, but lower-power class AB amplifiers distort in much the same way -- their distortion curves will just be "slid", in entirety, toward the left side of the graph.
The important point is that the distortion at very low power (left end of the graph) is almost 20 dB higher than it is just before clipping (right end of the graph, just before the point where the curves suddenly shoot upward vertically). So if you're connecting your 99 dB sensitive speakers to this amplifier, and it's spending all of its time below 1 Watt, you're experiencing about 20 dB more harmonic distortion than if you used a low-power amplifier with just enough headroom to handle transients.
Too much of a good thing is a bad thing. Unfortunately, that even applies to too much power.