LETS COMPARE TUBE AND SS AMPS. TECHNICAL

Oh Boy, here we go!

I would suggest some background reading.

I would seek out the chapter on amplification in Robert Harley's "The Complete Guide to High End Audio" for a general and relatively easy-to-understand discussion on amplification and some of the differences between solid state and tube amplification. I'd also read the section on speakers (because amplification is simply driving a load).

Then, I would go to the Atma-sphere website and go to the "Papers" section to read the paper titled Debunking Common Power Amplifier Myths and the other titled Competing Paradigms in Amplifier and Loudspeaker Design, Test and Measurement.

Knowing how tube amps create their "power" and how transistor amps create theirs, and understanding how speakers present a load to each particular kind of "power" will make things easier to get through the Atma-sphere papers though they may be able to be tackled on their own.

First of all the Almighty set ALL watts to be equal to the product of Voltage and Current or physically Work per unit of Time.
The power P that is measured in Watts can be consuming and giving and the remaining power dissipates on heat.
Tube amplifiers and Class A SS amplifiers are only (approx)20% efficient since the remaining 80% of power goes onto heat.
The mentioned 'sonic watts' can be described as SPL that is measured in dB(usually guitar dudes know what it realy is). Decibel is a logarighmic relative value that compares no sound to the actual sound. SPL can be measured also at particular freequency and that's where all the Tube/SS confusion burried as the 'Holy Grail' for some folks arround here.
Normally tube output devices have very high output impedance and amplify voltage that suppose to be converted to current using the output transformer to satisfy nowdays speaker voice coils. Transformer is the device that converts variable electric field of an input coil into the variable magnetic field and the output coil has the induced electric field from the variable magnetic field. The input and output coils of the transformer are actually inductors that have variable impedance depending on frequency. As the frequency drops, the reactance is minimal and impedance of the inductor approaches actual resistance of the wire. In this case the voltage accross the input coil terminal becomes MINIMAL as well as magnetic field across the primary coil! Another words by nature there's hardly any lower-end extention and 'visible' spectrum of it is substantially less than corresponding SS amplifier. So placing 'in front of each other' 100W tube amp against 100W SS amp obviously SS will seem to sound more quiet, but if measured SPLs across the 'visible' frequency spectrum, SS will have it larger in both ends of a slope.
As to the speaker voice coils, lower frequencies should be hadled with much higher current than midrange.
In tube amp transformer would act rather as high-pass filter thus distributing a larger portion of an output power onto substantially smaller frequency range giving the 'illusion' of so called 'TUBE WATTS'.