It sounds great to me! They quality of sound is definitely improved from the stock unit as well as the volume level I am able to play it at. I did not replace any speakers though so it is still lacking in the bass department but I never crank my music loud so it doesn't bother me. I just enjoy a good level while driving and it sounds very nice and clean.
I'm not sure what to tell you about the reverse thing. I just hooked mine up and the PDC comes on when I go into reverse and goes away after I pull it out of reverse. Never comes on otherwise. Maybe someone else who knows more about the mechanism of this function can chime in...
2000 528i steptronic