Well first off, the general wisdom here is if you already have enough power to hit the spl you want adding an amp won't really change anything. Clean power is clean power and most competently designed amps should be striving for the same goal- accuracy. It may help your AVR run a little cooler tho. When I added a Monolith 7 I didn't notice any significant changes to sq, but I'm not afraid to turn it up from time to time. You actually added a less powerful (than your Denon in 2 ch rating) amp for your fronts which seems like going a little backward, if anything.
If you're looking to improve overall sound quality that's going to be in your speakers (subs included). Whether you upgrade or work on optimization, positioning and integration. I'll tell you right now the glaring weak link in your setup is that subwoofer and I'd be focusing on upgrading it before even considering more amplification. You have a solid receiver with good power already.
All that said, you certainly have enough speakers to where I could see justifying some outside amplification for your front 3 to take some of the workload off your AVR, but would not expect any significant or audible improvements. I think 3 Outlaw 2220s would be the way to go, tho "reducing manufacture count" isn't a part of my consideration. I prefer matching speakers, especially the front 3 for consistent voicing, but matching electronics isn't necessary at all. Aesthetics and compatibility would be the only real reasons for that, imo.
Also if adding amplification I wouldn't bother unless you double down on power and you're getting pretty good bang for buck with Outlaw. They seem to run that 3-Fer deal with those all the time. It takes a doubling of power for every 3 dB of gain. So going from ~100w to 200w will give you a 3 dB more total spl, but again, no difference in sq (unless you're hitting limits now). Check out this spl calculator. It's kinda fun to play with and will give you an idea of the relationship between volume and power.
Every time I link that I end up playing with it for a few minutes, lol. I would absolutely be looking for better subwoofage first and foremost tho. Everyone underestimates good bass. Smooth, clean bass from a proper sub does more than just add thump. It gives everything more depth, texture and detail, and can elevate the entire system. Replacing my Klipsch subs with something from HSU made more difference to my overall sound quality than any amplification has done. It was a real eye opener for me.