I failed EPA once with a massive 111DB, what i did is i got the exhaust shop (the one that did the test) to make up a 2 1/4 inch pipe with a normal muffler to replace my cannon. So i had a 3 inch turbo back right down to near the muffler which then went to a 2 1/4, through a normal oval muffler. It just passed at 89DB.
So if he wanted me to pay for the custom muffler pipe he made it would have to pass