[MGRMLN]

I also have the Bimmertech MMI wired CarPlay module so I'm not sure why they would say it isn't compatible.

The Spotify app with the stock BMW is essentially "Spotify Connect" which streams Spotify directly into the car and NOT through your phone. Sadly, until they go lossless in the fall, Spotify is OGG/Vorbis compression, which is lossy and IMHO, doesn't sound all that great.
I believe Spotify will charge a surcharge to have lossless however. Apple Music however just announced they have moved to lossless and high resolution Dolby Atmos for the same fee as Apple Music. Between Tidal, Spotify and Apple Music, I'm likely only going to keep two services...