The problem is that Traktor doesn't recognize each soundcard as one unified unit and can only manage one soundcard. You need to use a utility like ASIO4ALL to create an aggregate soundcard (grab verison 2.10, not 2.11, I had some problems with it and won't suggest you try it.)
Once you have ASIO4ALL installed, you can select it from the task tray (near the clock) and make sure you have both of your CDJs recognized and selected as soundcards. Within Traktor, you'll then use ASIO4ALL as your soundcard and you should see all four of your outputs.