if your'e using bluetooth from a phone , to the h/u, with android auto, my understanding was that the audio is re-encoded by the phone, maybe transferred at effectively ~160Kb/s mp3 quality, then decoded on the head unit, so you have lots of audio quality degradation, versus running spotify, say, on the head-unit, with no 'losses'
You can try and use a better (near) lossless codec on the phone, or, maybe have it bitstreamed (ie you do no transcoding) to improve bluetooth.
(some earlier thread discussions if you search xtrons)