Reply to Kontrol Z2 questions

I am considering buying a Kontrol Z2 but i have a few questions first. I dont understand what it means by 2 + 2 tracks, and also if its good to go with Technic 1200 mk2s. And if anybody has any other opinions on mixers let me know. (I am a young beginning club DJ so i only need two tracks). and if is anyone is selling one $500 and under let me know! if you in the US that be a whole lot easier.)