Cannot for the life of me get the cue mix function to work on Mixtrack Pro.

I' switched to Traktor months and months ago from VDJ, but I just decided I should suck it up and learn to beatmatch by ear. But in order to do this effectively, I need to be able to use the Mixtrack "Cue Mix" knob in order to match them before mixing them.

This function won't work in Traktor, the knob doesn't do anything. I've tried multiple mappings including Traktor preset ones and custom ones. but no matter how I set things up, I cannot beatmatch in the headphones.

Any tips? Is this an audio settings thing? It worked just fine in VDJ