Thanks, Mark!

I have updated my example code here:
https://create.arduino.cc/editor/tfabris/4c5eea9a-1462-45d7-908d-81a5bb6b0d90/preview

It contains code that successfully gets track/album titles up on the car stereo's screen using the BlueGiga WT32i development board. I still don't have anything implemented on the Empeg side to actually get those titles, but the bluetooth side of it is functional.

I highly recommend getting one of those WT32i modules and using it to interface your empeg with your new car. Now that I've got most of the quirks worked out, I think this is the best bluetooth module for this task.

Here's what I've learned, and it's all incorporated in to the current state of the example code linked above:

- As Shonky pointed out, there are some important settings for configuring the bluetooth chip to identify itself as a certain class of device. Without that being set correctly, there will be unexpected behavior.

- Once those settings are correct, then the bluetooth module will receive certain notification queries from the host stereo. Your code must correctly respond to all of those queries in turn, and if your responses are wrong, you won't get the next query in the chain.

- The host stereo has to query you for the track title metadata. It comes late in the initial flurry of messages after first connection. If you don't answer all of the messages correctly then there is a chance that it might not ever get around to querying you for the track titles.

- The problem where the AVRCP communications seems to "hang" for 30 seconds or more seems to be related to the class-of-device settings and the message responses. Once I got my code correctly identifying the class of device and responding to the messages, I no longer had a problem with the "hung" AVRCP messages.

- There are other pieces of handshaking you have to do. Pairing with a new device can sometimes be tricky for example. I have code in there which mostly works for these purposes but I don't have a wide range of devices to test it out on.

- You'll need an external way to command it to erase the bluetooth chip's paired devices and start over again. I have implemented this as a button in my prototype, but if you're doing it, it could be a hijack menu command for example. This is all in the example code linked above.