To setup two turntables on the DJX750, follow these steps:
1) Plug into the left and right PHONO RCA ports on channel two.
2) Switch the selector on channel two to PHONO.
3) Repeat steps 1 & 2 with the second turntable onto channel three.
4) Turn the ASSIGN A switch to 2
5) Turn the ASSIGN B switch to 3
Now you can use the crossfader to move between turntable one on channel two and the second turntable that is plugged into channel three.