Ach! Intuitively I can see (perhaps) what might be going on: high Q speaker + high damping factor power amp => too much of a good thing in that the amp is great at controlling the woofer that has already been damped by the speaker cabinet. So, I can see how this reduces the bass - the woofer excursion is curtailed very quickly by the low impedance of the amp.
By having a higher o/p impedance in the power amp, only the speaker cabinet controls the woofer excursion as the power amp is "sloppier" in this dept.
No wonder then that the Berning ZH270 sounds best w/ the Merlins w/ its feedback at the "low" setting, which creates a higher o/p impedance & a lower damping factor vs. the other 2 settings.
By having a higher o/p impedance in the power amp, only the speaker cabinet controls the woofer excursion as the power amp is "sloppier" in this dept.
No wonder then that the Berning ZH270 sounds best w/ the Merlins w/ its feedback at the "low" setting, which creates a higher o/p impedance & a lower damping factor vs. the other 2 settings.