seems to me the logical conclusion you came to should have been apparent from the very beginning. I'm guessing you're like me, somewhere above novice but nowhere near "knowledgable" when it comes to the automotive world. That being said, even when I converted my "Mazda" Probe Turbo KLZE from FWD to RWD it cost me a fortune, I was young and naive, what can I said. Common sense states this simple fact: If the car you're wanting to swap parts from shares -0- structural / mechanical / chassis features, then odds are you'll have to be a tycoon of some sort to afford the fabrication.
-end rant
side note: MS6 > STi. personal opinion anyways - test drive both before making a decision though