It’s all possible to connect a midi controller a stand alone controller or a usb dj mixer like the Numark m6 usb.
you have to use a splitter or an external soundcard. If you use the splitter, just map the sound config to external mixer and assign your channels appropriately. if you use a soundcard, you can run 1 channel thru built-in and the other thru the soundcard. Good luck, hope this helps
