Rick, the only thing I can think of is that Audyssey has detected very high peaks in your room (room modes) and is attempting to level them.
It's also possible, if you have never used "room EQ" before, that you are used to bass over-load. As a result, a more linear level of bass may be sounding too weak for you.
A couple of thing to try:
1. Turn sub B off and set sub A to 70dB. Turn off sub A and set sub B to 70dB. Now turn both on and see how close you are to 75dB. Repeat in small increments on each sub until you get to 75dB.
2. Let the Denon do all the bass management by turning the subs' cross-overs to max (150Hz?)
