Does your system in your car have both bluetooth for phone and media audio? If you go into your bluetooth settings you should see Call Audio and Media Audio.
I have a car that is 5 years old and I do not have media audio. I also have a Samsung S4. I've been trying to get the voice to text to go thru my phone's speaker. Taking and placing calls are handled thru the Handsfree Link in my car.
I also tried an app called ********** and no luck with re-routing the bluetooth.