Cue problem

I recently bought the U-Mix contol 2 and the u-mix44 usb audio interface. Everything works fine and I like this kinda mixing. (I have been mixing with cd players) But I have a problem with the cue. It seems that it doesn't work at all. I have plugged the headphones into the U-Mix44. And when I try to cue a channel it won't play through my headphones?? I hope someone can help me