Virtual DJ is software for virtual, computer-based audio and video mixing. There are a number of versions and they range in price. The "Pro" version of Virtual DJ allows users to set up Midi/HID external controllers like external turntables, CD players and mixers. Setting up a mixer allows users to perform the mix using hardware rather than the virtual interface provided by the software. Using the hardware provides a more traditional mixing and DJing experience.
Change the output from "Headphones" to "External Mixer" in the Virtual DJ Config. screen. The Config. screen is at the top right corner of the skin.
Verify the channel assignment drop-down is at the default, which is "Left Deck/Left Channel" and "Right Deck/Right Channel." Adjust the soundcard from Mono-separated to the 4.1 card option.
Plug the cables into the black and green outputs of the soundcard. Plug the other end of the cables into the line inputs of the mixer.
Click on "Apply" in Virtual DJ and then click on the "Options" tab of the Config. dialogue box. Disable the virtual crossfader -- from the left-hand list, set the internal crossfader to "Disable." Click "OK" to close the dialogue box. The audio will now flow freely from Virtual DJ to the external mixer.