I so happened to have ended up with both these av receivers. The Denon is a 2013 model and the onkyo is 2 years old. The onyko has more input outputs etc. My question is more on everyone opinions on the audio (and video) QUALITY of each. which one should I keep.

Theoretically, they should be pretty much on the same par for quality. It mainly comes down to preference of features/connections/interface/remote...

I have a 709 and love it, but I wouldn't hesitate to use a similar Denon.

Sorry that I don't have a clear cut answer for you.

Can you sell both and upgrade? Ha! Just teasing. Either is probably fine. Stuff comes out of the same factory doors these days.....

Which has more watts into all channels? Winner for me.

The denon barely cracks 20lbs.... 20.94

The denon review at whathifi is hilarious.... "Minuses- occasional brightness at high volume."

More clipping than a barbershop.

More watts doesn't mean much. It has been talked about a few times here that 125 watts vs. 100 watts isn't key at all, for example. Now clipping, and features are another story.

would be worth selling one receiver and adding a power amp. I would have to sell the Denon because it has no pre-outs and the Onyko does. I have M22 fronts vp 150 center EP 175 sub and QS4 surrounds.

Gar, welcome to Axiom. It would only be worth it if more power than the 709 in particular was capable of supplying was needed. It's highly unlikely, especially with the sub carrying the low bass burden, that more maximum power output is actually required. At typical comfortably loud average output levels the Axioms use about 1 watt. Brief peaks require much more of course, but not likely more than the 100 plus watts which the receiver can supply at inaudibly low distortion levels.

Ample headroom is already highly likely present. Buying a separate amplifier which would provide yet more headroom isn't economically sensible; unused headroom is simply that: unused.