I have an E39 from 1999 (UK model) with Professional audio system which includes a 6 CD changer and an amp in the boot. My audio system is stuck on a rather high volume and won't adjust from the vol knob or steering controls. Also, the tone cannot be adjusted and fader and left/right speaker selector are gone. However, the radio reception, casette and the CD changer are working fine. I got another head unit (from a 1998 528i) which plugs in fine and works but the same problem persists. My dealer won't tell me where the problem is but will change the whole system at the cost of an arm and a leg (and take the old system as well!).
I have been advised aftermarket systems but am not sure if I like the way most of them look.
Has anyone experienced a similar problem and what's the best way out?