2012 Prius Four JBL Bluetooth Audio with iPhone 6-- no sound

I have the JBL GreenEdge head unit with Nav and an iPhone 6 with the latest iOS. When I play anything through Bluetooth Audio, I get no sound. The display shows the song title and the song timer counts up, plus I can touch pause and play and they seem to take effect. In other words, on the display and on the phone it looks like all is working, but I get no sound. When I do Bluetooth phone, on the other hand, it works fine. This problem has existed for over a year and I've always just shrugged and plugged in the USB but I really want to get this working so I don't have to always have the USB cord handy.

What I've already tried to do:

1. Reboot the phone
2. Turn the car on and off
3. Delete the pairing with the phone (on both the phone and the head unit) and then add it back

None of this has helped.

Anyone else seen this or have any other ideas?