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.
I have run my engine w/forced induction and NOS. I have a built short block that has been decked, ductile cylinder liners, forged pistons, etc. Also, I am using an Motec engine management system with a big Paxton fuel pump. Don't go over 450hp without the short block mods or you will fatigue the block within 10-15K miles. E-mail me directly if you would like info on getting the engine work done or info on engime management alternatives.
Not to press the point to death, but you should not even consider doing something like this without a real programable engine management system. The piggy-back fuel or timing controllers are good enough to handle one or the other, but not forced induction and NOS at the same time. At least not reliably.
The kit was a barely used custom fabricated setup using twin Garrett turbos,custom piping, Trust/Greddy blowoff valve and wastegate,liquid to air intercooler,(aftermarket fuel and oil pump(don;t remember the brand)). I got it from a guy who bought a nsx with like 4000 miles or somethin with that setup, but he felt that a n/a motor was fast enough for him so he sold the whole thing to me. I'm gonna have it tweaked a little here and there by Larry of the NSX Modified shop in Huntington Beach.
Hmmm...there was this one guy that used Bell's twin turbo setup with a 70 Shot NOS system on his 96 Red NSX-T, He lives in Southern California, and has attended many cars show, I must say, one of my favs!!! He was featured in a Turbo Magazine...I think last year...I still have the magazine in Mint Condition...I love his car...I'm going to post a pic, some might not like it, but I love what he did to it! Sorry I don't have any other pictures or of the engine, cause I couldn't find any, and I myself was stupid and I didn't take pictures of the car when I had a chance, I actually got to talk to the owner once..he's real cool. Well, here's the pic!!!!
I have no idea where that liquid to air intercooler is going. Right now all the parts are in a box and needs to be pieced together. I also still might have to custom fabricate a exhaust and will not know the specs until I bolt on the turbo and see what kind of configuration I need.