My plan B, that I am using now, is a bluetooth adapter that plugs into the 857d's audio output, and then transmits the audio via bluetooth to the Ford Sync Bluetooth Audio input. Here's what I'm finding I don't like about this arrangement:
1. For some reason the Bluetooth Module never connects back up to the car right away, even if it was the last device I was using. Also, for some reason, it only seems to work if some other bluetooth signal was already communicating with the car first. This means that every time I get in the car I have to turn on the little bluetooth module, connect my phone via bluetooth audio to the car so that it starts playing music through the bluetooth stream, then I have to switch the bluetooth source from my phone to the module, while playing, before I can hear the receive audio. That's a lot of screwing around before I even get out of the driveway!
2. The bluetooth module needs to be charged every so often, or used while plugged in to USB power. No biggie I thought - there is a 12v power jack behind the location that I mounted the remote head. I figured I could just plug everything in, and leave it plugged in. NOT! The noise that is introduced in the audio while the bluetooth module is charging is horrific! this means that I can't use it and charge it at the same time, unless I want to listen to all kinds of noise on my receive audio.
3. The audio quality is noticeably worse through the bluetooth module. If I tune the car's radio to an FM broadcast station, and then tune my 857d to receive the same broadcast FM station, the sound quality is noticeably worse when I switch back and forth between the two.
4. The audio through the bluetooth is delayed. I'm used to pushing a button on the radio and getting an instant beep, confirming my button push. Going through the bluetooth, there is about a 1/2 second delay.
While I'm sure I could adjust to item 4, the combination of all of these things made me decide to attempt Plan C.
Audio Plan C
I quickly jumped on the Amazon listing and added my answer to the question - as someone with personal experience - this will NOT work with a car - at least not a Ford with Sync.