My previous car had a USB socket that supports MP3s on a flash drive (well also an Aux input), and I navigated using my phone and its speaker. So the MP3s play in parallelwith the navigation prompts (from different speakers - car and phone).
My new car has Android Auto, I can play music from the phone, but whenever Google Maps wants to say something the music is paused...
Luckily it also has the music player outside of Android Auto and the 2 things can co-exist (with audio ducking)..