BFD + Spd-Sx + NI Traktor Kontrol S2

Hi Guys!
I have a question.
My setup is based around DJing with Spd-Sx for live sampling and drumming.
So I have my Computer connected to a NI Traktor Kontrol S2 and to a Spd-Sx.
The output audio needs to go through the NI Traktor Kontrol S2, because I need to hear through headphones that are connected to the controller when I choose to.
The problem with BFD, that It only lets me choose the Spx-Sx as the sound interface, and only output through it.
How can I make the BFD output go through the controller?