Hey,
Not meaning to answer for 19 inch NSX, but the only twin turbo "kit" I am aware of would be the one made by BELL..(ie..Corky Bell proprieter).
As far as wether u can add nos on top of forced induction,I dont see why not, AS LONG AS THE COMBINED MAX HP is below the threshold of engine tolerance...my understanding is that this figure is in the 425 - 450 HP range..anything above that will require some engine modifications to prevent the engine from being fatigued to the point of meltdown.
Obviously, to me at least, this kind of work should be done only if both BELL and RM?? (for the nos...) can agree it wont blow up your car....Good luck.
Goldy