Rick, is the Denon prompting you to manually set the sub to 75dB at the start of calibration? If so, the final calibration should be within a dB of the manual setting. If you have multiple subs, set each so the sum total will be 75dB. I have three subs and each is set to 70dB. The sum total is 75dB for my room.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated