I recently did something similar to what you are proposing. I initially added a 282 and HCDR to my Nait XS, so just using the power amp section of the Nait. It worked perfectly fine, no obvious issues with my speakers. I felt no compulsion to upgrade after that so left things that way for quite a while. A fairly priced 200DR became available and I decided to go for it as it wasn’t going to cost a great deal (in HIFi terms) after the sale of the Nait XS.
It wasn’t a huge upgrade. The 200DR had more control and nuance compared the Nait XS power amp section. The Nait sounded a bit warmer, a little blurry in comparison, but nice and comfortable sounding, the 200 being a bit more transparent. In the grand scheme of things, it was a move in the right direction, but one day I can see me going for a 250DR (I have some other upgrades planned first though).
I can only imagine that the difference between a NAP200 and the power-amp section of a Supernait 2 would be smaller than what I experienced. Having said that, I’m not a big fan of the Supernait 2, I find it a bit forced and brutish, which is why I bought a Nait XS in the first place. The 200DR is definitely more on the nimble and agile side of the spectrum. So you might appreciate that aspect of its character.