The only option I can think of that will give you "Race Car sounds" i.e. popping and snapping when wanted and quiet highway for trips and retain any hearing, is to do one of two things:
Add the 4.8is rear mufflers and tips like RickyBobby = OE performance sounds and engineered solution with no down sides. Down side $$ unless one finds a donor car.
OR use a electrical cut out pipe and valve that would dump all exhaust before the mufflers (You will need two). This will give you NOISE ON DEMAND feature. Perfect for when you need a NASCAR or (old style) F1 fix. Think WIDE OPEN EXHAUST SOUNDS and you will get the image.
Totally illegal in the US for street use but people run then all the time.

See link: Exhaust Cutouts at Summit Racing

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2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green