I just purchased a 2009 Z4 sDrive30i. It has the HD Radio with 8 speakers (midrange and tweeter in doors, subwoofer in kick panel, and midrange in side panel behind seats). I would like to keep the radio, as it is integrated into the iDrive, but upgrade the rest of the system. Does anyone know if HD Radio has a separate amplifier, and if so, where is it located?