The B&B comes with an X-pipe. It combines the exhaust note from both sides of the engine delivering a deeper, more robust sound. "Wow, that doesn't sound like a 6 cylinder".
The Greddy (The SP model I still believe looks incredible) has an H-Pipe. This keeps both sides of the exhaust much more independant of one-another. The exhaust note sounds much more like you would expect the 6 cylinder to sound.