Set the 57 into audio mode. So if you have your outputs from SL1 to channels 1 and 4, set them to (cdj or phono) and then your selection of Audio or Digitial knobs (both beside the Gain knobs) or on the 57, turn to A1 and A4, not using the D mode. From there, you should HEAR the output from the SL1 through headphones. Making sure the 57 is independent of itself. When everything is fine, plug-in the USB from the 57. From there, this is where you really learn how to manage the audio outputs from each device. Do it, troubleshoot it, write it down or remember it. Do this at home or in the studio. lol

I do this with a buddy of mine at gigs every week. I have my 57 set up to use channels 1/4 & have the SL1 connected to 2/3 of the 57. Next, just change the inputs on the mixer to audio 1 (L)and audio 2 (R).

Thanks everyone, i figured it out, it makes it so much easier now at gigs to just have both laptops set up the whole time!