Your catback can go on where your stock one comes out. If you want to get the most out of your exhaust, you'll want to get a header and a highflow cat, like a Carsound cat. Remember that the diameter of the header collector to the cat to the exhaust piping should never constrict and always stay the same diameter if possible or expand.

For example, you have 60mm piping on your exhaust? Go 2" collector (unless you find a 2.25" collector), 2.25" cat, then your 2.36" or 60mm exhaust. That way you have no bottlenecks and you utilize your system to its greatest capabilities.