After downloading and installing the mapping into Traktor you will only need to select 900 Nexus In as you cannot set a midi out single with the Nexus. Make sure the midi ON button is lit which is located on the top right corner of the 900 Nexus above the Effects display screen for midi mode to be turned on. 

I'll have a picture describing what the features of the Nexus does soon.

LINK CUE - Shift for Key: Once on, each color FX knob will control the key adjust inside Traktor for it's respective Deck/Channel (1-A, 2-B, 3-B, 4-B). 

FX CUE - Shift for Tempo: Just like key adjust, once on, each color FX knob will control the tempo adjust for its respective Deck.

FADER START BUTTONS: The fader start buttons are mapped to load the selected track for each deck. Do note! The 900 Nexus does not have a gate feature so buttons are always set to toggle mode. In this case, when you have loaded a track, the Fader Start button will be lit, you can hit it once to turn the light off without any issues to get ready to load the next track in that deck when ready. I call this the "Double Tap." It was wonky at first, but I now find it as a good visual to know I have a live track loaded since I use Traktor with "Load into Stop Decks Only" Disabled. 

This is the first mapping of my series of 4 different mappings I have developed for the Pioneer DJM 900 Nexus that will really unlock its usability with midi and give some fun and useful options that both controller and DVS DJs can add to their live sets and performances.