My car stereo has an aux input jack as well as the Bluetooth hands free profile. I couldn't stream music over BT, but could use the hands free to talk on the phone, send texts, and all of the other voice commands that the phone can do. The problem was that if something is plugged into the headset jack on the phone, that's where it looks for voice input, which means that if I was plugged in to listen to a podcast or music, and I received a text or phone call, the phone wouldn't hear me to have it read the text, or the person on the other end couldn't hear me talk, unless I unplugged the aux cable from the phone (which killed the incoming text - it would no longer read it to me).
I picked up a Logitech BT receiver, which has the A2DP (streaming audio) profile. It is plugged into the car stereo's aux input, and the phone connects to both the car stereo and the Logitech device, since they're on different protocols. I made sure to NOT get one with the Hands-Free protocol, as I don't want to be talking to a small box when I can talk through my car stereo. Using it, I still got ground loop feedback if I was charging the phone (which I like to do in the car, since I have an hour-long commute, so why not take advantage of the time), so I also picked up a ground loop isolator to go between the Logitech and the aux input.
Because this Logitech device is not made for use in the car, it doesn't automatically reconnect with the phone when I get in and start the car. I have an NFC tag sticker in the car, and I programmed it to open the BT settings, so it's easy to tap on the phone and connect. This device does not come with a car adapter, but I happened to have one that had the right size plug and right voltage. The polarity was backward, but having been an electronics student in high school (and I went to school before boards became swap-out-disposable), it was trivial to switch that up.
I am VERY happy with the combination, and in fact I just ordered another BT receiver (same model), so I can put it in my living room, and I'll get some small speakers to mount alongside the mantle of the fireplace (the big stereo is in the man cave).