Reply to next upgrade/ piece of gear?

current gear: Numark Mixtrack (Soon to upgrade to a Kontrol S2), Midi Fighter Classic, MDR V700 Sony Headphones, and my laptop

so what should i upgrade after my mixer? or should i get something like a Midi Fighter Pro? Suggestions plz?

ps- btw there are three of us together who DJ at the same time :P (believe above and beyond)