slippery,
i think youll agree with me that the amplifier is not about the sound output, but about the sound quality.
Hmmmm.
Have you seen measurements on that Denon? Where exactly on the measurements do you see something that makes you suspect poor SQ from that AVR?
If the AVR amps can drive the chosen speakers to satisfying levels without clipping, and has enough headroom for dynamic spikes, then there will be absolutely no benefit of external amps.
The only reasons you would NEED an external amp is if the AVR amps can't drive the speakers to satisfying levels without adding distortion, or if you had 2 ohm speakers and the AVR amps aren't 2 ohm stable.
Again, try it with the AVR FIRST, then if you aren't where you want to be, then consider an external amp.
If the AVR amps drive the speakers without any problems, then the $ would be MUCH better spent on acoustic room treatments (i.e. an area that has not yet hit diminishing returns) or better speakers, vs an external amp where you are already approaching diminishing returns