After update, car radio stopped playing audio through USB from my Samsung S5 using AOA

I've bought a Pioneer radio for my car that supports Android Open Acessory (AOA) 2.0. I was happily living with it playing my music through the USB cable to my Galaxy S5 phone. High quality connection and charging at the same time. Just one cable. It was great. To configure it, it was just necessary to select the correct USB connection type (MTP, if I remember well). Now here comes an update to Android 6.0 and everything stopped working. It still charges, but I can't make the music go through the car speakers. The USB options now are inside the developer mode. I've tried all the options, but can't make the music go through the USB cable. My old Moto G, with Android 5.1, successfully connects and plays through the USB cable. Any fix, workaround, or help to debug is appreciated.