I am looking into getting a vance and hines slip on for my 2009 kawasaki zx6r. I currently have an M4 moto gp slip on and dont have any of the stock exhaust from the previous owner. Would I have to buy something extra because based on looking at pictures of the vance and hines slip on it looks like I would need the pre muffler, is that true or could I just switch them out. Thank you