Thanks for the link and comment, MikkiJayne.
I removed the speaker completely from the door, and the bracket and the speaker housing is made out of one piece of plastic. Although, looking closer at the BOSE speakers, it looks like they are screwed into at separate bracket like those in the Audison link.
In the afternoon I received a message from Prestige Motor, that the BOSE speaker will fit directly and will work. He confirmed that they have done it for a customer. Obviously it won't be like a complete BOSE system without the proper amplifier and also the BOSE system has to two speakers in the parcel shelf (and a center treble in the front) that the std sound system doesn't have.
I feel tempted to go on with this...
