Bottom line is that F/I won't sound as nice as a high revving N/A motor- not matter what exhaust you put on it. This is of course subjective.
Here's a clip of the F30 M3 and an E92 M3 on the ring, recorded on the same camera. E92 wins by far in the sound department IMO (20 sec mark):
This was also the case with the F40 and the F50. F40 was faster, but the F50 was a symphony of beautiful, high revving, N/A music: