I have this Problem.
I always hear Musik on my runs. The Headphones paired only with my watch, Phone stays at Home.
I hear the "pip" - Sound (Musik Volume goes down, the same as in my 965). But after that, when the Garmin Voice speaks the Musik Volume goes Up again. So you cant hear the speaking.
I have Auto lap at 1km. But i can only hear the Voice clear, when music ist changing a Song or it is a more silent Song. On the 965 the music Volume stayed Low until the Garmin Voice hast finished.