Welcome to the forums. Be sure to go ahead and post the "before" pictures so we can see what you're working with.
ST204 and ST205 exhausts are not compatible on each other. The exhaust is routed differently due to the AWD components. There are very few bolt-on catback systems for the ST204 so sadly, your best option is to buy the individual pieces you'd like and have an exhaust shop weld you up a completely new system.