Lots of points raised, I'll make some brief comments.
Larry, blind listening tests have shown that THD has to be more than about 1% to be detectible when listening to music rather than pure test tones. The THD numbers for any of the units which we would seriously consider are far below audibility when operated within their designed limits.
Speakerchooser, the 120 watts of your Yamaha are measured according to the FTC regulations with two channels simultaneously driven at full rated power for at least five consecutive minutes. The three front speakers don't "share" this. The difference between 120 watts and 200 watts is 2.22dB in maximum sound output; e.g. if a peak could be played at 110dB with 120 watts, it could be played at 112.22dB with 200 watts. Both figures are higher than likely to be needed for home use.
Mike, the controlling element is voltage, not current. For 1 watt into 8 ohms a bit under 3 volts is required(V[squared]/R)and about a third of an ampere(P/V)rather than 60 amperes.
Bernard, the calculation of power required has to take into account both the reverberent and direct sound fields. This is as was described in the Voelker and Linkwitz material that was linked in my first reply here. They should be studied carefully(especially the Linkwitz power calculation) to understand why less power is used than is sometimes thought.
