I wonder if you can tell me how you got the iPhone to stream music over Bluetooth
Sure. I use a PS Engineering PMA 8000BT audio panel with integrated BlueTooth capability. I chose this over BT in the A20 as it is considerably more capable. See:
PS Engineering :audio select panels
This audio panel is superb in every respect, and not all that expensive to retrofit especially if you already have a Garmin 340 or other PSE 8000 series audio panel.