You seem to assume the unit is only power supply limited. Based on many review lab measurements I have seen, many HK and NAD amps are actually more so amplifier limited than power supply limited, while the opposite seems to be true for Yamaha AVRs. Example: at a given price point, the HK model would likely put out the same or more watts in ACD than the Yamaha, but in 1and 2 channel driven, especially into 4 ohms the Yamaha will almost win by a wide margin every time. I provided links to HTM, HCC, S&V lab measurements in the past so I am not going by just saying.
Another point, let me beat 3 dB to this, your figures do not factor in amp efficiencies at different load, power factor (cosine of phase angle between voltage and current phasors, impedance characteristics etc.) As a rule of thumb okay.
just my 0.0001c