There is only 1 exhaust on the driver side. It would be nice to get dual exhaust but probably not possible because there is no space for the passenger side.
Perhaps try getting one side from an E60 m5?
I am going to do this with my brother's 745Li to see how it sounds. The 745 exhaust has a vacuum activated flap that keep it quiet, you can also open it all the time, has a nice rumble to it.
E38 5.4L V12