I have being testing my new Fenix 7x for a week, and I have found that the sound quality (for both Spotify synced music and local MP3 files) is terrible. Sound is distorted, with a lot of noise and hissing (sounds like a low quality MP3) , and it is a total deal breaker for me.
I have a Fenix 6x, and I have compared both (with two different pairs of bluetooth headphones: Sony and Sennheiser, and with the same music over Spotify and MP3 files) and the quality in the Fenix 6x is much better. It is not an audiophile device, but no distortion or noise, and you get clear sound.
Have anyone experience the same problem? Hope they can fix it with a firmware update, because it is really annoying, I cannot rely in my Garmin to listen to music (for a 1000€ watch...).