I was suggesting a single 1500 with three channels.
The advice I've given you is based on my in-house "testing" of M100s, M3s, M5s, M50s, 160, EP800 and QS10s - all v4. Also ADA-1000 and ADA-1500. I upgraded from M80, VP150, EP600 and QS8 - all v2. I've written extensively about the v4 and love them all!
I am in a 4,200 cu. ft. space with the fronts spaced 12 feet apart and I sit 13 feet away. In 2.1 using Spotify Premium or Tidal HD over my Chromecast Video (HDMI), my Onk is not good enough. With Netflix via my no-so-smart TV, my Onk is barely good enough. My Onk is more than adequate with Blu-Rays via my PS3.
There is of course no problem with you trying out just the new Denon to see if you will be satisfied. I am telling you though that 30 additional Watts is absolutely nothing given your sitting distances. You'll also be moving from M22s to M5s; the M5s are slightly less sensitive.
With regard to ADA-1000 vs. ADA-1500, the ADA-1000 in 2.1-channel is no better than my Onk when using the M5s. Multi-channel is of course a different story because the ADA can provide gobs (375W) of peak power to all channels whereas my Onk completely chokes. My Onk's power output is similar (and may be better) than the 4500.
So try just the 4500 and go from there.
P.S. When everyone was saying gobs of amp power are needed, I thought they didn't know what they were talking about. After all, my Onk never shut down so why would I need an external amp? It wasn't until I got the ADAs and started listening more critically, and took measurements to confirm, that I realized my Onk was compressing with high quality music. Most receivers employ dynamic compression to prevent shut-downs and distortion. Unfortunately the compression also reduces the peaks and that is just not as satisfying as listening to the full signal. The ADAs do not compress; they just gracefully temporarily turn off that channel's output letting you know their limit is being exceeded.
I find the ADA-1000 is a great choice with M5s if you are sitting 8 to 10 feet away in a small to medium-sized room. The 1000 is also a great choice with higher sensitivity speakers like the M100 for greater listening distances.
