What component is responsible for dynamics ?

Everything in the system, from the quality of your AC, to the size/layout of your acoustic space, can and will affect the dynamics of what you hear.

I remember reading a post many years ago on Audio Asylum where a recording engineer measured the compression of dynamic peaks in various loudspeakers, and found a strong correlation between loudspeaker efficency and preservation of dynamics. Unfortunately that post has apparently been removed so I can't post a link to it.

Duke
dealer/manufacturer

The system as a whole and it's synergy with each component and connection are responsible for how dynamic your system is.

I think it would be speakers efficiency first, as Duke mentioned.
And guess, who's speakers are 108 dB efficient?

It will be the amplifier,if it's tube,it's circuit design and component used.Next is sensitivity of the speaker,the higher the better.