The ninja from bug/blob will fit on the 06. No probs, I actually sold mine before I got the 06 thinking it was different fittings. I got the car checked out and exactly the same CS and backbox size.
So I had to go buy a new exhaust Centre Section and Afterburner Vortex. Probably louder than what you are looking for. Like previous posts if you are after subtle burble CS and prodrive, sport backbox. When its better weather over the weekend ill get a sound clip up of the vortex on an 06 STI