What component is responsible for dynamics ?

Increasing music dynamic is like increasing the acceleration of a car. There are two ways to achieve the objective. Lessen the weight of the car (high efficient speakers) or increase the horsepower (amplification chain). An example of a very dynamic car would be a F1 car. A Nascar is less dynamic than a F1 but both have similar top end speed (max spl), but very different performance.

If your looking for dynamics a compression driven horn loudspeaker will do it the more horn loaded the better. But for many they are to large or costly.PA,vintage or used can save you with cost. The macro dynamic has more to do system synergy. And over all quality of the whole.

"what one component will offer the most beneficial change ?" I'd say the speaker.

From my empirical knowledge:

Doing the math, I used to think that a 10 watt amp mated with 100 db speakers would produce the same dynamics as a 100 watt amp with 90 db speaker. I mean, it's math. 2 + 3 is the same as 9 - 4. Didn't work out that way to my ears.

I had 1000 watt monoblocks driving my Maggie 3.6's (85 db). In the same room during the same time period, I had 10 SET watts driving some custom studio monitors (low 90's). No contest. The 10 wpc/90+ db was more dynamic than the 1000 wpc/85 db.

I suppose it depends on your "strict" definition of dynamics. The 1000/85 could play louder, that's what 1000 watts can do. Dynamics to me mean how fast a speaker can go from, say, 60 to 85 db. To me, a higher eff speaker does it better than a lower one.

Onemug,that`s a good example.This is what I meant by more spontaneous and instantaneous with music`s ebb and flow, much better dynamic contrast.

High efficiency horns are indeed the easy key to dynamics, but you are right - many cats in the game. I have highly inefficient Apogees and they are the most dynamic speaker I ever owned (I never owned horns though) - paired with the right amp I should add.