Well tha NN-XT is actually stereo and i forgot how many outs u get, but u can route about 5 or 6 samples loaded into one XT to a mixer like u wanted...U really dont need a splitter.
What youl do is this: Once u have your XT and all your samples loaded into it...Then youl need to add a mixer for tha channels your about to route. Once your mixer is ready, go to yer XT and highlight tha first sample in tha window - then look at what sample output is has. Tha very 1st one should be 1-2...Then click on yer second sample in tha window and go down to tha sample output knob again and choose 3-4, and keep going up for each new sample after.....
Then, TAB back and youl see all those open outs. All u gotta do now is simply drag yer 1-2 to tha 1st channel on yer new mixer and then repeat these steps for tha other samples.