I have DSP/NAV in my X5 and was very unimpressed with the sound when listening to both CDs/MP3s and the radio.
This past weekend I installed an aux input and with my ipod hooked up to it with the ipod eq set to loudness I actually have a new sound which emanates from my stereo, bass ! Its not exactly what i would call deep or very accurate bass but it actually has some now.
Looking into 3 series for my next car, not sure I will fall for BMWs "premium" stereo option this time unless they have vastly improved.