What component is responsible for dynamics ?

Not sure what speakers you have, but if they have a sloped baffle make sure that they are properly levelled so the rake of the baffle is optimally aligned, as intended by the designer. (Speaking from personal experience, this improved dynamics for me.) Also try more severe toe-in as well.

Going back to what Jafox said, after your speakers, I've never heard gear provide dynamics in the way the CAT gear does, now I had the preamp/amp so I don't know which was responsible, or more so, but I would describe dynamics as the special quality of CAT gear, matched by few.

Saki70, You’ve put your question to the forum in a general way and received a lot of interesting answers, but I’m wondering if you are also trying to find the dynamically weak link in your system. If so, Sidssp is correct; we need to know more about your system. And then, there might actually be one identifiable component.

Sure : Reference 3A Di Capo i speakers
Primaluna Prologue II integrated amp
Granite 657 CDP

I am in a small 10ft. X 11ft. room with wall to wall carpet and 8ft. ceilings . I use some room treatments , 8th Nerve , consisting of pads in the corners and above the speakers where the walls meet the ceiling . I have the speakers and listening position set up on the diagonal with the listening position and speaker seperation set in an equal lateral triangle of 6ft . The speakers are firing staight forward , no toe in .
I play the CDP through the tube side using the stock tube.
The amp has had the tubes rolled to EH EL34's on the output and Mullard 12AX7 & Radiotechnique 12AU7 on the input . I am using a M. Wolffe Source P/C and ZSquared au/au IC's .

Hope it helps.

Individual components won't guarantee proper dynamics in a system. In order to preserve the dynamics in a recording it is essential to have a system with suitable gain structure between components. If you can't turn your volume control past the 9 o'clock position without your system getting too loud, then your gain structure is off. Similar mismatches can occur between the preamp/amp or amp/speaker. It's not as if there are perfect interfaces between components, but there are wrong ones and those will degrade your system's dynamic performance.

Regarding loudspeaker, I don't think that higher efficiency is what makes some speakers sound more dynamic, instead I think it's related to larger driver area and the amount of air that is excited. It's my observation that loudspeakers with twin 15" drivers have greater dynamic capabilities than a loudspeaker with a single 6" cone. The reasons why are obvious and if you wanted to reduce it to a simple statement -- small speakers won't sound as dynamic as larger speakers, assuming appropriate caveats.