Yep. I get that. It's frequency based, and subjective. Supposedly overcoming the deficiency in the headphones. So the idea is to make all headphones sound the same and thereby the reference quality is reached? I question whether that is what is required. Surely then, different headphones, without being 'altered', may give a different sound and 'feel', which would allow for a little more individual approach. Why have some excellent, but very different headphones available, if all you going to do align them? But I do see the value in using this approach as well, so I am not disagreeing with your choice, just pointing out these things are very much subjective. If everyone as you say uses this, then I will stand corrected, but I have my doubts.
NX it seems is more about 3D spacial placement and relative position to the 'monitors' in an ideal mixing room. It's quite a different thing to frequency response. The two plugins would probably work well together.