Heat/Efficency of Speakers

...does the power usage scale with the volume and demands of the speaker?

Yes, absolutely, in the case of class AB, and even more so in the case of class D. For class A, though, the AC power drawn from the wall outlet will be determined by the amplifier and will be essentially the same all the time, with the power that may be supplied to the speakers at any instant subtracting from the power that is dissipated (converted to heat) in the amp. (But as stated above almost all of the power supplied to the speakers will then be converted to heat in the speakers).

Also, keep in mind that most of the time under most circumstances just a small fraction of the amp’s power capability will be utilized. Brief dynamic peaks in the music will typically result in much more power being delivered to the speakers than the time-averaged amount of power that is delivered. Although different recordings can differ greatly in that regard. Recordings that are dynamically compressed to a severe degree (which is particularly common among pop and rock recordings) may have less than a 10:1 peak to average ratio of the amount of power delivered to the speakers, while there are some classical symphonic recordings having minimal or no compression for which that ratio may be more than 1,000:1. In the latter case very little power will be supplied to the speakers, on average, and hence a class AB or class D amp will not generate much more heat than when idling.

Regards,
-- Al

To make this a bit simpler, Class A amps will typically generate the most heat because they draw full power all of the time. Class AB amps will generate less heat but the amount will vary depending on whether they are heavily biased into Class A (more heat) or less.  Class D amps generate the least amount of heat.  The situation where speaker efficiency will make a significant difference is if you go with very high efficiency speakers, because you can then use a very low power tube amp. 
















c

Ok, assuming I only require 2W of power at the speaker:
Class A will dissipate heat equal to its power consumption
Class AB/D will consume a tad over their idle power consumption with D being closer yo idle than AB.
Correct?

Maximizing my speaker efficency is my first priority. Also correct?

Red funeral,
As others have pointed out,  the amplifier is by far the greater contributor of heat in the room. Find a class D amplifier that in your opinion sounds good and go in that direction. 
Charles 

Your friend must pull his hair out at your inability to accept a simple, experienced answer. He is right, but you seem determined to prove your thought process, even though it has little operational  applicability.  A simple question resolves the problem, "Does this amplifier run hot?" Beyond that all the hypotheticals are meaningless. 

It reminds me of the story of two men who are in a hot air ballon and become lost. They see a small town, lower their altitude and ask someone on the ground, "Where are we?" The helpful citizen yells back, "You are in a hot air ballon!" Technically correct, and completely useless information. If I may be so bold, you are seeking technical information witch is fairly useless to success in building the audio system (i.e. cool running) you desire. :(

Class A and tube amps typically run warm to hot, but there are exceptions
Class A/B you can find hot ones, medium and cool running ones
Class D never runs hot; at least I have never encountered one which runs hot

Of course, all this has little to do with sound quality, which ranges up and down among all classes of amps. I suggest that seeking an amp which operates with the least percentage of heat loss is a grand way to build a mediocre sounding audio system. 

A discussion of maximizing one's speaker efficiency also has nearly zero relation to the question of how hot a room becomes with use of a certain class or model of amp. :(

You are way overthinking the issue, and it seems you struggle to accept simple, straightforward advice from experienced persons. I wish you success.