The sound system in my MX is definitely better than the one in my M3 (both are premium package). It just has more depth and control over bass frequencies, which are slightly muddy in the M3. Not that the M3 sound is poor, I think it's actually pretty decent and way better than what you would typically get standard (or cheapish Bose upgrade) in other cars in this price range. The sound system in the MX is top notch. Really very good indeed and considerably better than I've experienced in the MS too. Maybe the bigger cabin volume helps. I do like Spotify as a music source too. No messing about with phones or files etc.