What component is responsible for dynamics ?

Rok ;
Yes one correct answer would be nice . But usually just a major consensus is the best that there is .

It depends on what you are currently using and your room. Without knowing the details, it is impossible to tell.

I think you have to start at the source. The dynamic range of a cassette tape is 90db or lower at best, whereas the dynamic range of SACD (I believe) approaches 110 db. Db's being a logarithmic scale, this is an incredible difference. If it's not at the source, good luck reproducing it down the line.

But still if I were to choose one component, I would say turntable in purely analog system and power amp in purely digital. To put aside horn speakers for the moment.

Not surprised that high efficiency speakers are top of the list of suggestions but there's more than one way to skin that cat(love being non-PC).

For speakers, you can divide the question into 3 parts; transients, bass slam and SPL (volume). The latter being more associated to allowable distortion. Oversimplified, often it is "bigger is better".