I have to admit that the denon is not as easy to set up, i made this change too, but once done the denon is in a different league to the sony.
Are you sure it is not as powerful, have you got a SPL meter to set it up to reference level ???
the sony at reference level sounds louder because it is being really pushed, where as the denon still has somthing left in it.
I could never listen to my old sony at the same sort of levels that i listen to the Denon at. But as you say at the same actual (say 75db) listening levels the sonys do SEEM louder than the denon, you are right.
In stereo mode a have tested the denon against a my quad77 amp and at the same levels the with a SPL meter the denon sounds louder than the quad.