That speaker is apparently a backup ASSIST speaker in case the MOST link is severed in an accident, and if your car came without ASSIST it wouldn't have the speaker.
With my 07 with HiFi and Assist, the chimes came through the head unit going to the amp. I don't think it's a coding thing, I think it's a HU change. I know when using the Mobridge DA1 early on, later E90's would lose chimes even though early ones would not.
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