M5/M5C stock exhaust is not loud enough, even the M Sport exhaust option is not loud enough.
I went with
this exact setup and let me tell you the video does not do it justice, you can actually "feel" the exhaust in person when you're behind the car.
Fly by view. Even just doing the primaries and secondaries on stock exhaust will make it sound much better and deeper,
you'll get a nice turbo whine too.