Plug your CDJ's cables into the input sockets on the SL 1. The left deck goes into input 1, while the right deck is input 2. (When facing your decks, these inputs are on the back of the interface. When looking at the back of the interface, the right deck goes into the input on the left, while the left deck goes into the input on the right. See Resources for diagrams.)
Connect the outputs to your mixer using the RCA cables included with your Serato setup. Left and right deck line outputs connect to their respective (left and right) line inputs on your mixer. Set your mixer to "Line" level.
Connect your "PHONO" inputs on your mixer to the left/right respective "THRU" outputs on your interface. Using "THRU" allows you to switch from Serato Scratch Live to your own CDs at the flip of a mixer switch.
Connect the interface directly to your computer using the provided USB cable. Do not plug it into a USB Hub or splitter.
Connect your CDJs to the deck inputs on the SL 3 interface. Flip the "DIP" switch down for "line" for CD players.
Connect your SL 3 outputs to the respective line inputs on your mixer.
Connect the SL 3 AUX output to to an AUX input on your mixer (or an additional line input) if you would like to output the sample player. Connect an AUX input on the SL 3 to an AUX output or additional output on your mixer if you plan to record.
Connect the interface to your computer using the provided USB cable.