Carplay & Music sound quality terrible compared with Carplay & Spotify

Hi,

I have a Carplay enabled head unit in my BMW and have happily been using Spotify Premium over Bluetooth with it; the sound is great and I've always been impressed by the ease and simplicity.

Having started using more Apple products such as Airpod Max's and Pro's, I've started enjoying the Apple Music capability more often and so have decided to subscribe to Apple One, giving me access to Music properly.

Although I recognise Atmos (or indeed lossless) is pointless in a car, I've got an expectation that the High-Quality setting in Music delivering AAC at 256kbps should be more than able to deliver as good as a sound as the Spotify 'Very High' (320kbps). I recognise that Spotify uses the Ogg Vorbis codec rather than AAC when in High Quality, however, this should be irrelevant.

The problem I have is: When playing a song on Apple Music through Carplay, the mids and bass are poorly controlled - making it sound awful. If I play the same song through Spotify over Car Play, it sounds significantly better.

I don't believe it is an issue with the CarPlay unit or the physical sound setup as I can reproduce great quality playback of a song using Spotify rather than Music.

Unlikely to be a Bluetooth issue as you'd get poor playback for everything...

I have tried turning off Dolby Atmos and tried High-Efficiency mode for mobile streaming, all to no avail. Furthermore, I've ensured that Sound Check is OFF, and the EQ doesn't have anything enabled (although I understand EQ doesn't affect CarPlay).

Has anyone else experienced this? Have you managed to work out what is causing it?

I'm going to try my iPad shortly and see whether that has the same issue to rule out the device.