I just bought a new Chev Silverado that has OnStar, I want to change the HU but will I be able to keep the OnStar abilities i.e. turning the stereo down when I hit my phone button, and giving me directions ect ect. Is it just as simple as getting a Receiver Interface Adapter?? I know Besy Buy told me it was $270 JUST for the damn Adapter...... they dont sell it by itself and so on a $350 HU they wanted $270 for the Adapter, $100 for the harness plus $150 for the mounting kit and labor. Like hell Im paying $500 to install a $350 HU. Any help would be great..