If the amplifier is unable to follow the waveform presented to it (which is the source of all dynamic contrast) then it will distort.
Perhaps a bit counterintuitively, if a particular amp is **more** dynamic than most others (for example SETs) its also because of distortion. In the case of SETs up to about 20% of full power their distortion is pretty benign. But above that point, the higher ordered harmonics become more pronounced. Since the ear uses the higher ordered harmonics to sense sound pressure and because transients is where most of the power is, when the higher orders show up on the transients, the ear interprets that as 'louder on the leading edges' IOW more 'dynamic'.
Its a simple fact that when audiophiles talk about dynamics, about 90% of the time they are really talking about distortion, and you can safely replaced the word 'dynamics' in that conversation with 'distortion' without changing the meaning of the conversation.
Put another way, amps that sound more 'dynamic' are very likely to do so out of distortion and nothing else. The dynamic character of the music should come from the source, not the amp, that is if the amp is accurately reproducing the signal!
All so true....great post! I would only add that great amps that sound more dynamic can also do it due to extremely low distortion and better execution of instantaneous power delivery.