I explored this topic when I first bought my 540i, I wanted that screaming V8 sound without having to deal with it all the time.
I removed the exhaust from the car and cut out a 6" portion of each pipe after the cats, before they joined into the one pipe at the y resonator. I did this to allow fitment between gas tanks and to allow me to use only 1 e-cutout instead of 2.
Welded in the y pipe and ran the cutout with electric valve for a few months and loved it. silent when you want, and screams at the flip of a switch.
Unfortunately my motor seized up on me, and I ended up just running the cutout wide open all the time until I took the car off the road.