DC, i think the Pioneer would sound fine with the m3's, but sonically probably no different than the Denon. Are you saying you want to use the Pioneer for HT applications? If that is the case it would lack all of the decoding for HT.
For music only (2ch) the Denon should do just as well. I recently pulled out my early 90's JVC Pro Logic receiver and it drove my 80's just fine.