People are going to say its not a great sound system, but it really is. 825 watts is the best n the class. Actually both of them are great (I only know from loaners with my iPod plugged in) I think the M has a bit more bass, and the subs are located under the seats so you at least feel it a bit more. With classical music, the M can handle the highs about more than the logic 7 system.
2016 340i M-Sport 6-MT(on order)
2013 335is (still have)
2011.5 M3 ZCP (traded in)