Problem with DJM 750 Mk2 and the Preview of Traktor

Hello

I have just purchased a Pioneer DJM 750 Mk2 and use it as a external mixer with Traktor Scratch Pro.

The problem I have is that I can't listen with the headphones connected to the DJM 750 the Preview listen of Traktor (not the cue of the desks that I can).

The configuration I have in Traktor  is:

- Audio Setup-> Audio Divice ->  DJM 750Mk2

- Output Routing -> Mixing Mode -> External

- Output Routing -> Output Deck A -> DJM 750Mk2 Out 0 & 1

- Output Routing -> Output Deck B -> DJM 750Mk2 Out 2 & 3

- Output Routing -> Output Deck C -> DJM 750Mk2 Out 4 & 5

- Output Routing -> Output Deck D -> DJM 750Mk2 Out 6 & 7

- Output Routing -> Output Preview-> DJM 750Mk2 Out 8 & 9

 So, as you can see I have the Preview in output 8 & 9 of the mixer but it doesn't work.

If I change the Preview, for example, to output 6 & 7 of the mixer, I can listen to it through the deck D, but I haven't been able to make it work in the (I believe) correct outputs 8 & 9.

Any of you has the DJM 750 Mk2 with Traktor? The Preview works? Am I doing something wrong?

Thank you very much in advance!!!