Spotify via USB 1 or USB 2

Has anyone tried using Spotify on their iPhone with the USB connected? It works perfectly fine over Bluetooth, but the sound quality and volume is terrible, pretty much have to get the volume up to 50 just to get some decent volume. When plugged into USB, and when i go to the commander knob and select USB 1 or 2, nothing comes out.

This is on the nicest 2017 Silver GT in all the Fraser Valley region.

Thanks for any help!!

I haven't tried connecting with USB for music, but I suspect that when it's connected that way it's seeing your phone as a storage device (looking for mp3 files etc) not a streaming device.

I have a Nexus 6p and don't have any Bluetooth problems, music plays clean and loud. Are you keeping your phone close to the dash with no obstructions? Bluetooth has a short range and low bandwidth that can barely cope with data rates for music, any degradation of the signal will affect the sound. Do you have the volume turned up all the way on your phone? Do you have the latest version of your phone OS and Mazda infotainment software? Do you have an older phone that doesn't support the newer versions of Bluetooth required for decent music playback? These are the things I'd look at.