....the fact of the matter is that Porsche designed the engine, transmission, and entire exhaust system as a unit, and that entire unit was placed on a "shake table" and the harmonic balance of that entire unit was matched to the rest of the car and acted as a tuned balancing system.
That's why the muffler is attached the way it is with that big cross beam.
That is why any two muffler setup will sound horrible inside the car.
This FACT is well documented in the Porsche history book "Excellence Was Expected."
The whole dang powertrain is matched to offset the chassis harmonics and null them out.