About the exhaust mod discussion, I learned the hard way with mine. I already had a header, and went to Budget Muffler (first mistake) and told them I wanted 2.25" piping from the cat back and to put in the oval (non-bling) Magnaflow muffler I had. The retard there called it a fart can, which it obviously isn't. They took out the resonator after the cat (without asking), which made the car sound like absolute ass. It sounded so bad I felt physically ill driving home with it in that state. The muffler was ~80$ from Summit, 120$ for custom piping and labor, and then another 40-50$ for the resonator that they had to put back in. It sounds 100x better with the resonator.
Now, with that said, if I had an MS3, I'd delete the resonators, because it sounds like this:
http://www.youtube.com/watch?v=xXwJE6bsL40&feature=related
The turbo acts like a muffler, so the MS3 will naturally be quieter, and not raspy. Plus without the resonators, it sounds like a Subie flat 4, and I think that's a big plus. Go for it!