The slip-on is designed to mate with your stock, factory headpipes (which are very good - they're light, stainless steel, and carefully designed for power).
You cannot convert it to full system to "save money".
It might be possible, though unlikely, to do - but will cost you more to special-order all the parts than just buying full system.
Bottom line:
Just ride it.
If you want full system, think LeoVince...
Also, I hope you have budgeted ~$400 bucks for a PowerCommander and $75 for K&N if you go full system.
Not sure why you desire anyway. Gixxer600 needs torque, you don't really have any to trade for more horsepower.
You already have horsepower...