I'm surprised. The sound system is one of the best I've had, its fairly accurate and detailed in the mid range without having an overblown and boomy bass.I've also come to realise that the "advanced sound" is not very advanced on the premium. If it's better than the standard I'd be very shocked. It's suppose to have a sub. I can't hear any lows really. I have an onkyo TV setup (dated) but even my old 220d I felt had more lower. Where is the so called sub woof!? I'm not a metal fan at all but lows are those you feel but don't really hear. I'm afraid I'd say BMW beat MB on sound!! Had a TT before too (hairdresser yess but drive a Quattro and it remains a firm favourite) and it's sounds I thought had more balance.
The worst I've ever had is the std system in the 3 series BMW, I've had better sounding transistor radios.