Does your car have a tune? Is the check engine light on? Recently bought a catless STi in from FL, and it passed w/out an issue @ a nat'l chain. As long as you're OBDII and not throwing a check engine light, and haven't recently, you should be fine. So I'd suggest you hit up Mike Benvo.
If not, put your stock exhaust back on and drive the car until it recalibrates and the check engine light disappears.