I know what you mean, my M5 also had an exhaust and it was music to my ears. But then I totaled it.

Eisenmann does make the exhaust in two levels, race and sport. Sport tends to be on the quiet side, but I don't know how it'll sound on the X5.

You could always replace the center resonator with a smaller muffler. I know that e53 4.4/4.6/4.8 guys this.