FYI, our cars use manifolds with the turbine housing built into the manifold. Good luck finding a replacement. There are few out there but you will never get the boxer sound.
HOwever you do have one of the quietest exhuasts. I suggest getting catless downpipes and a louder exhuast. You will soon forget about the greatness of the boxer engines. I miss my STI. but I have learned to love my 335i with no mufflers....