^have to disagree with sol. There is so many reasons I could think of to have 4 deck control. Besides that isn't the thread topic, he was asking how it can be achieved, not why he shouldn't do it. This could be achieved by practically any 4 deck mixer (eg djm 700, 800, 900), running your cdjs to 2 channels, then using a traktor soundcard to run the other two channels into it. You could then use a basic midi controller (eg traktor x1) to control these two decks. Another possibility is getting traktor scratch with an audio 8/10 and running all 4 decks through your computer. That gives you traktor features (hotcues fx loops etc.) over all 4 decks. Hope this makes sense as I'm a bit tired writing this lol. Any q's reply back and I'll explain myself clearer