JB, those suggestions from pro amp makers unfortunately have little relevance to home audio. Using speaker ratings is essentially meaningless when the question is how much power is needed for a given sound level, not how much the speaker could take continuously without suffering damage. Generally the answer to how much is needed is far lower than the maximum speaker rating. Actually, the minimum suggested(e.g., 10 watts by Axiom for the M80)may be closer to a realistic answer to the question.
As to the Crown power calculator, the problem with using its results for home listening, which you mention, has been discussed in some detail here previously when its general use was suggested without adding cautions. The formula shown for the calculations(specifically the 20xlog factor)shows that it's simply applying a 6dB per doubling of distance sound level reduction, which is only appropriate for an omni-directional sound source in anechoic conditions. The calculator page itself contains no caution as to this source of inaccuracy. Only in a separate discussion of power needed
shown here does Crown mention this, and only near the end, under "Other Considerations" is this key point briefly explained. The 6dB correction factor suggested there results in reducing the calculator's result to 1/4th of its previous value, although for some reason even then Crown doesn't explicitly point out that a much less powerful amplifier can be bought, but merely comments that the 6dB correction can be added to headroom.
