I have recently purchased an A4 (B6) Cab and i have noticed the sound quality isnt that good. I dont have BOSE but it sounds like far too much treble and not enough base. Even when i add more it sounds even worse.
I had the same system in my old MK4 Golf but it was called an MFD. That sounded far better
The only thing i can think of is that the volume for the phone (which i dont have) makes a difference to the sound. Could it be that the system thinks the phone is connected?