Have you confirmed definitely that the problem is the output from the player? Which signal are you using (digital or analogue)?
Have you checked that you haven't accidentally bumped the input switch at the top of the channel on the DJM (the one that toggles between CD/Digital, Line/Phono and USB)?
Have you tried switching the channels that the players are plugged into (i.e. switch player 2 to channel 3 and player 3 to channel 2). Just to confirm where the problem lies?