Disconnect your turntables' RCA jacks from your mixer, but keep the turntables' ground wires connected to the mixer's ground terminal.
Get out your multicore cable. Connect the "Mixer Line In" red and white RCA cables (on the multicore) into the corresponding red and white "Line" ports on the mixer. Multicore cables are segmented cables; each segment has several RCAs on one end and an XLR on the other. Each cable is marked.
Connect the Mixer TT/CD RCA cables (one of the RCAs on the multicore) into "Phono In" on your mixer (for turntables) or the other "Line" inputs (for CD players.)
Connect the remaining female RCA on your multicore to your turntables or CD players by inserting the male RCA cables into them. You have connected channel one of your mixer.
Repeat the steps for connecting channel two of your mixer.
Switch your mixer to "Phono" (for turntables) or "Line" (for CD players.) Play a regular record or CD (not control) to make sure you have configured the set-up properly. You can also play your control vinyl if you don't have a regular record; the control vinyl or CD should make a high-pitched sound. (Your set-up should work as if you were playing an analog set without Traktor or your computer.)
Connect the red, black, yellow and white RCAs of the Audio8 multicore cable into the corresponding Channel A inputs on the back of the interface box. Repeat with the second set of red, black, yellow and white RCAs for Channel B. Channel A connects to the left deck, while Channel B connects to the right.
Connect the XLR cable (on the end of the Audio8 DJ multicore cable segment) from Channel A to the female XLR cable attached to mixer Channel 1 (on the end of the mixer-segment multicore cable.) Repeat these steps for connecting Channel B to Channel 2.
Connect the included USB from the Audio8 DJ to a USB port on your laptop.
Push the "Input Mode" button on the interface until "Control Vinyl" (turntables) or "Control CD/Line" (CD players) is selected. Ensure that the USB LED is permanently lit.