micky wrote:

Wow. That's so obvious, now that you said it. The cable is in the car
so I can't check it now.

I don't know that I have line-in. I have microphone-in. That will
probably be good enough?

Yes, I do have a headphone jack. Like on all good phones. In fact, in
the car before I tried bluetooth I was using the cable to the AUX input
of the car radio and it worked for 2 or 3 days (rental car while
traveling) and then it stopped. Now I hear a low sort-of rumbling
noise, even when I turn the car radio all the way up. My roommate is
going to lend me another cable, atlhough a simple MP3 player continued
to work fine with the AUX port. Who knows, maybe it's the cable
anyhow.

(I had trouble pairing the phone with the car (even though I'd paired
it with my PC at home and two in the ear speakers.) The word Mazda was
supposed to show up on the list but didnt'. I finally got it. )

Well, you don't want to try it with Bluetooth, that's for sure.

I got Windows 8.1 to show signs it could do a sink, using
the Widcomm stack that comes with my Broadcom BT4 dongle.
But, once the item is inside "Playback Devices" in Win81,
it stays grayed out.

On the Win10 side (which uses the Microsoft stack), I couldn't
even get any evidence at all, it supports A2DP source (to pair
with A2DP sink on the Win8.1 machine).

The devices paired. They showed the six digit pass codes
on each PC. But nothing profile-related seemed to work.

I replaced Win10 with Ubuntu, and tried again, and Ubuntu
wouldn't even show audio output over Bluetooth as an option.
And for extra joy, the Win81 side stopped showing audio sink
as an option while connected to Ubuntu.

So all the Bluetooth garbage hardware has gone back
into respective boxes.

It doesn't seem to be permissions.

As long as this stuff doesn't provide logs, we'll never know.

Paul