A couple of thoughts here:
If you are considering the purchase of an M23, that’s roughly a $3k investment. I’ll use that as a "baseline" for additional "financial headroom" in your system.
I’ll go along with others who have suggested room treatments. You can do alot for a fraction of your available budget. This is also consistent with your inquiry related to adding more power. Reducing reflections and quieting down those sounds that like to hang around for a while will improve the perceived dynamic contrast in the room. This may provide the sonic impact you are looking for, without adding more power.
One needs to ask what your goals might be in wanting to add more power? Typically, this is done when a system does not have the energy levels the listener is looking for. 2x the power = noticeable increases in SPL. However, if the desired outcome is in the deep bass region, this task may be better served handing off the responsibility to a powered subwoofer rather than "exercising" the NS-5000s woofers more aggressively. They won’t play as low as a high quality sub, and will, literally, die trying. Something to consider?
Also, I’m going to put this out there although some may disagree with this premise. I found that Class D amps are particularly picky about power delivery. That is to say that they sound much, MUCH better when supplied with excellent power. I’d start with replacing the wall plug with something better than builder grade, and pay close attention to power distribution/surge protection/filtering. Last, but certainly not least, try a variety of premium power cords to see which provides the best sonic benefit(s) to your system. IF, after doing some and all of the above, and you like what you are hearing, you might try replacing the 10A slow blow fuse with an "audiophile" fuse. Many on this forum (myself included) have found these to quite effective. Most offer return privileges if you don’t like what you hear. I’ll just state that unless you’ve done most of the above, you’ve not experienced the true sonic character of your NAD.
In summary, for less the cost of an M23, there are other options that will provide a more sonically rewarding experience. IF you do ALL the above and still want more impact then, by all means, add the M23. But, first things first.