Charles, when a calibration is done, whether manually or by an auto-calibration system, the adjustments made to the receiver trims for the various speakers compensates for differences in their sensitivities as well as factors such as different locations. No, once the difference in sensitivity has been taken into account, that difference remains the same at higher or lower sound levels than the one at which the calibration took place(typically around 75dB)and the compensation still applies; otherwise there'd be little value in bothering with calibration, since it would only apply to one volume level.
The usefulness of Audyssey Dynamic EQ arises because of the lesser sensitivity of our ears to bass and treble at lower volumes, together with a lessening of surround effects, but this has nothing to do with the difference in speaker sensitivities.
