So here is a wrap up regarding the frequency response of this line of amps. We know that all the boost models share the same HPF (subsonic, rumble filter, etc), and it is set at 30Hz with a little boost above that. We also know that there is a seperate bass boost circuit to give the boost that is spec'd for each model. The HPF and boost are summed (combined) to give the overall frequency response (plus the phase and low-pass adjustments of course). So for those still interested in these, and having the desire to modify/customize the response, here are a couple of pics to help. Best thing to do is to defeat the boost circuit altogether, then tweak the HPF as desired, and as is common with other plate amps.
This pic points to the two resistors that need to be changed to tweak the HPF. They are located close enough to the edge of the pcd (near the led) that it shouldn't be too difficult.
This next pic is the back of the preamp pcb, and shows the two jumpers needed to defeat the bass boost circuit.
Here is the frequency response of my 200-6, after defeating the bass boost circuit, and modifying the HPF to an Fc of 13Hz, Q = 0.6.
We haven't had any user feedback about the non-boost models, but my suspicion is that they share the 30Hz HPF, but their boost circuit is configured for no boost. I will try to confirm this when my backordered 300W model arrives.