Is it true the Bose systems in the w140's were changed during the years of production? I know the head units were different but what else and why?

I heard from some people it sounded better in the earlier years than the later years. How come?

__________________
99 C43
98 S420
99 C230K
01 C240

As far as I know, it was only the head unit that changed from the Becker to an Alpine. The wattage increased at the same time from 240 to 245 due to the increased capacity of the Alpine.

__________________
Jonathan
1998 S600
2001 E430
1994 E320
1991 560SEL
1994 Turbo R