Official comment
Traktor doesn't allow multiple audio interfaces to be selected -- you'll need to use ASIO4ALL to create an "aggregate" device which can access both the DJM and MASCHINE audio devices as the same time. Once ASIO4ALL is installed, select both of your hardware devices (and all of their outputs) to be active, then within Traktor, select ASIO4ALL as the audio device and assign the channels accordingly.
Unfortunately that's all the support I can provide for this issue as it's not a Pioneer DJ related problem.