I wouldn't really say that Dirac room correction makes a better "stereo" sound. The quality stereo sound is more due to the analog output stages and power supplies in the processors. It's difficult to say which of these may be better. Both have pretty good power supply sections. Both "appear" to have switching power supply for digital (which it actually very typical).
The NAD is built on a modular and expandable platform where you can plug-and-play different modules for different things as new technologies emerge (such as HDMI 2.0 and HDR as well as Dolby Atmos). NAD does have firmware upgrades, but not very frequent (the latest firmware upgrade is dated "03/04/2020"). There is a Dolby Atmos module for NAD that adds 4 height channels, but they are all RCA output.
The McIntosh MX123 has XLR outputs for 13 channels (including Dolby Atmos height channels). This might be better depending on what cables and amps you are choosing. McIntosh will not have firmware upgrades at all.
