Here's one more twist for you to try out. In my Pioneer, I can set the sound retriever (Called S. RTRV) to ON and this enhances both the lower and the upper end. I don't know what it's called on the Denon. It's purpose is to enhance lossy formats where the bass and treble are somewhat missing. I use this setting at times when I feel a need for a little extra oomph.
Edit: I found it in the Denon 2310ci manual on page 52. It's called RESTORER. There are 3 modes and off. Mode 1 is for treble boost only. Mode 2 is for bass and treble. Mode 3 looks like it's for bass boost only.
It takes away from the flat settings, but it might supply the bass you're looking for, particularly in the M22's.