one is a multisampler and one is a rex file loop player. depends on what i'm doing, sometimes it calls for the dr.rex, other times it calls for the nnxt. the nnxt gives you more controls over individual slices/samples where as the rex player is limited on editing individual slices/samples. you can also load samples and rex slices in the nn19 and the redrum. hit the help menu and read up on the modules so you can know what they do and how to use them. there is nothing like getting it from the horses mouth as opposed to other cats on FP who probably didn't read the manual either.
LevLove