Based on the above, and assuming your Denon behaves as the referenced one, I have to wonder if the differences you hear are simply a matter of differences in the bass management.
In your original post, you say speakers are set to small in Stereo 2.2 mode.
Based on BatPig's statement, when you switch to D/PD, the speakers are being switched to large (whether you intended it or not

).
The obvious thing to do is switch your speakers to large in Stereo 2.2 mode and see if you can still detect an audible difference.
Either way, the cool thing is that you have found better sound!
PS: I always knew your sound wasn't as perfect as you let on!
(Does it sound too much like petty envy to say that?
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)