Hey, thanks for that! It actually got me a bit closer. I am able to use a combinator in this way and get the two keyboards to work separately IF I use two Thor's for eg;. When I try to use one Thor and One NN-XT the controller on midi bus A always seems to send note-on to the Thor as well. The keyboard on midi bus B always works as expected. Just another spot of weirdness.
I'll keep hacking on this method and let you know what I am able to find. I would have thought that I could get pre-sales support to answer these questions since I won't actually buy the product if this doesn't work. I already own protools and will stick with that for recording. The live application of Reason, if it will do what I'm after, makes it worth the bucks imho.