How to connect Denon Mc3000 to Traktor 2 pro

I recently bought the Denon Mc3000 and traktor 2 pro. Installing traktor was no issue, and the driver for the controller was fine.

The problem is at the audio set up, I select external controller, Denon brand, and Mc3000. However at the audio set up it says check your output source, so I'm guessing I can't use a basic desktop speaker for the controller? Since it has one universal source instead of a L and R.

If that's the case, why can't I use my headphones? When I put a song on traktor, I press play and the track plays but theres no sound coming from anywhere, not even the headphones.


Also, whenever I connect my controller and turn the power on, my internet shuts off. This CANNOT be a power issue right? Since a controller is supposed to be connected to a laptop, and laptops don't contain nearly as much watts as a desktop.



EDIT:

The problem was the usb source so everything works now, the only issue is with the headphones. The sound works through the speakers fine, but how do I get it to work with the headphones? Unless that's only for cuing?