Hi,
I voted "others" but here's what I mean.
Either the Marantz or the Onkyo amps will comfortably outperform your Denon AVR so doing that is a great plan.
What I would ALSO do in your situation is LOSE the Denon AVR as you will now only be using it as a pre.
Buy a DEDICATED pre/pro to match up with the multi channel power amp you choose.
Marantz....Onkyo........Integra......Yamaha....and more!!!!
I GUARANTEE any one of the above will OUTPERFORM your Denon.
You are now running seperates and will really hear the difference.
Lastly, you will clearly be better off with either of the Power Amps you mention but why limit yourself to just those 2??
Work out a budget
Work out what to do with the Denon (sell, keep for other room...etc)
Try to listen to a few contenders
Take it from there!!!!!!
Cheers