So you are saying you had to increase the levels +12 or so to get back to the SPL you were at with the Denon alone?
Assuming has to do with either the pre out voltage of the denon and/ or the input gain of the AMP?
I've noticed this with different AMPs I have. My Outlaw/ATI AMPs give me the best results so far in this regard. I guess it doesn't mean like there is another wrong with boosting the levels to get back to the same SPL at a relative volume #. But psychologically it is defeating after buying an AMP that you have to work so hard to get back to the same loudness
(if this makes any sense)