How to connect a basic DJ system 

And with the Pioneer CDJ & XDJ multi players you can use one usb. So one deck you click usb and on the other deck you click link. But just make sure that you don't pull out the usb.

tnx bro

Can a laptop be added to this setup as performance or export?

So you connected everything without using a power AMP only a mixer , my question would be what's the purpose of a power AMP ?