u-mix44 problem. can't switch monitor sound

Hi, I couldn't find my answer anywhere so I'm going to ask. I am using a stanton scs3 system. I also hooked up the mixvibes u-mix44. My problem is that I have the headphones hooked into the mixvibes headphone jack and the master sound comes through them. I can not monitor individual decks in the scs3 system. if I switch the monitor buttons on the MIDI controller nothing happens it just plays the master sound. Any help???
Thanks Jimmy.
Thanks Jimmy.