Reply to Traktor S4 with VMS4

Hello ppl

Friend of mine own Traktor S4 controller and i try to hook up my VMS4 to S4 software, but i've got a problem :
I receive an audio signal only from one channel on my VMS4 i.e
if i choose in Output routing ->Output Master ch 1 and ch2 and raise left volume fader on vms4 i receive signal from deck A, and deck B (if i rise deck B volume fader), but if i raise volume fader on deck B, while deck A fader is down, there is no sound
if i choose in Output routing ->Output Master ch 3 and ch4 everything goes vice versa.

Any ideas ?

PS : sorry for my bad English ...

Edit : Traktor S4 has only internal mixing mode ...