What component is responsible for dynamics ?

It's the speaker ...

uh, the amp ...

uh, the amp and the speaker working together ...

us, and the signal strength coming from the source component ...

and of course the mastering on the vinyl/CD ...

oh yeah, and throw the preamp in there because, you know, it's in the signal chain and has gain too, unless you're running a passive and this discussion is moot to you.

:-)

Preamp, amp and speakers

The loudspeaker is the largest offender in reducing or expanding dynamic range.

Listen to some Klipschorns.

Then there's both macro and micro dynamics to take into account. Brute force macro dynamics are one thing, and you can find that with efficient speakers for the most part. But those micro dynamics are what truly raises a good system to great territory, and that means finesse in the entire audio chain.