Get the Denon because should your father-in-law ever get 4-ohm speakers like the M80ti's (or other brands), the Denons will drive them, and the Onkyos are iffy in that department.
But don't let Denon's gimmicky auto-equalization sway your decision. It's okay to use the auto-calibration for setting channel levels but turn off the simplistic auto-EQ. The latter is the latest marketing gimmick offered by a number of manufacturers. At Axiom we continue to get inquiries from customers whose Yamahas or Denons or Pioneers equipped with auto-EQ erroneously signal that their speakers are "out of phase" when in fact they are correctly wired.
EQing a room is tremendously complex, and even if you set it up for one location, the EQ will apply only to that one position. Shift to another seat on the couch or chair, and everything changes. . .The potential of primitive auto-EQ is to undo all the good design and linear performance of fine speakers.
Axiom Resident Expert