wattage

As I read your post Tennisdoc40, I was thinking about the SPL drop-off with each doubling of distance from the plane of the speaker...
I scrolled down & saw that Almarg had already addressed this point. :-)
I'm thinking exactly along Almarg's lines.....
To make the music flow effortlessly - meaning playback of all the peaks without feeling the music is contained - you will need a lot of watts. 1000X the spec'd wattage at 8 Ohms, just like Almarg wrote.

Ratio of peak to average power required, as Al said, is very
high. Amplifier's power specification alone is only useful
for listening to continuous sine-waves. Otherwise 10W
amplifier with big headroom can sound much louder than 100W
amplifier with small headroom. For instance, in class A amps
headroom is very limited. Higher output bias current would
make amplifier very big, heavy and expensive. Class AB amps
don't have this limitation - headroom can be higher.

In addition power specification are often very vague.
Continuous power of the B&O module (200ASC) in my class D
amp is 40W. FTC Power is 55W. Rowland rates it 200W while
Bel Canto rates it 300W. What is it?

This 1000x wattage issue is misleading. The math works and so does the logic, but it's not how your ears and brain hear it. Clipping and the dynamic compression that it produces can be very hearable and annoying, or it can be hearable and somewhat pleasant sounding, or it can completely unhearable. It depends on a number of factors.

Even with the newer class D amps, high quality-high wattage amplifiers are still expensive. In allocating money in a system I'm not sure it's wise to spend based upon what happens 1% of the time. I'm repeating myself, but a well designed 50-100 watt amplifier should suffice for the vast majority of circumstances.

As for playing the numbers game, you would also have to factor in the effect of heating of the voice coil. As you increase the current flowing in the voice coil, it heats up and resistance increases so that each additional increment of power delivers less and less increase in acoustic output (this is a major source of compression). Also, mechanically, as the drivers are pushed towards the limits of their excursion, there is an increase in the mechanical resistance which further increases compression. Hence, much more power is really needed that those simple formula suggest to get to a particular SPL level.

That said, for the most part, I agree with those who believe that the recommendations on power greatly exaggerate how much is needed. Give me quality over quantity any day.

I appreciate the feedback. I have a 100 wpc ss amplifier powering speakers with 91 db sensitivity and the woofer having it's own class D amplifier. I was demoing a 150 wpc amp of the same brand and preferred the sound of the lower powered amp, even though it's listed peak amperage was lower. Growing up, we thoroughly enjoyed music powered by a Sansui receiver at 30 wpc through 16 gauge speaker wire from Radio Shack.