I had TWE headers, high cat 2.5" pipe out to a Borla muffler. That was loud. But the car drove awesome. No throttle effort needed at all. Hard to explain.
Then I added a magna flow muffler to the mid pipe. That fixed the noise but I had no ground clearence. So I sold the Borla, moved the Magna Flow to the back (Kind of ugly) and had two resonators (2.5" x 12" and 2.5" x 18") installed. Worked great. Nice while cruising. Scary when WOT
Remember the Turbo of your old STI killed the harshness of the engine noise. Our engines are just raw.
ps did you notice you fuel milage dropped when you put the ehaust on your car, or it just my car? My car now has the stock y-pipe and cats. JUs the 2.5" out the Magna Flow (as listed above). My milage has not returned. : (