1) Launch DP3
2) create an stereo AUX track on your SEQ1 screen
3) click and hold on the input section of that AUX and choose a new stereo bundle> and then choose Battery 1-2 (or whichever NI that you have)
4) choose a set of ouputs on your output section...
5) launch your NI program
6) Now depending on which NI program you have - (please see your documentation) - but you must go to the Audio port of your program and choose "Digital Performer/ MAS" as yout Audio output -
7) then choose your sound or kit on your NI program
8) now toggle back to DP3

you are now ready to use your NI within DP