Other audio players such as Pandora, iHeart Radio, Musicolet, Shuttle, etc, all lower the audio/music volume when Android Auto Maps speaks directions, so you can hear the directions easier.
I have not found a setting in PlexAmp to do that. Please guide me to that setting, or take this as a feature request. Too easy to miss directions currently, as the directions and the music play at the same time and at the same level.