when i installed my second sub, i put the SPL meter at the MLP and rotated the phase knob on one of the subs, from 0 to 180 Degr. while playing the sub tone in the AVR.
as a result i gained at least 6 dB's in total output, just by adjusting the phase on one sub.
did you "turn off Audyssey" for real (out of circuit path) or do you mean you turned off Audyssey calibration?