Well the 4Trak has its own internal soundcard, so the audio interface isn’t necessary. Take that out of the setup and it may help you. Next, an XLR is a balanced cable, which essentially means you need two of them to get the full signal (a left output and a right output). By VCA do you mean RCA? If so, that is an unbalanced cable, which means it can transmit both signals with just one cord (that’s why it’s got two connectors, red and white–one goes in the left output and the other into the right).
As for the split cue, have you installed the 4Trak audio drivers? Do that first before plugging the 4Trak in or starting Traktor. After that, plug the 4Trak into your computer directly (without using the Focusrite interface), turn it on, then start Traktor. Start the Controller Wizard (it’s called something like that) and choose 4Trak as your controller. Finish the wizard and that should set you up correctly.