I've got a similar UK model (except mine is saloon rather than estate). On mine, I think there was a connector for each rear parcel shelf speaker behind the rear seat back (i.e. between the rear seat back foam and the metal panel of the boot). Note that mine had an Alpine head unit and an amplifier fitted, which may not have been stock BMW (so it's possible that the connectors were only there behind the rear seat back due to the installation of the Alpine stuff). Let me know if you want tips for removing the rear seat back - it's quite easy but not obvious.