Having a Range Rover P38 HSE, the sound system is a Harmon Kardon system, this is lovely, comprising of a head unit, amplifiers in each door, a sub base and 6 CD changer in the boot - the sound is really impressive.
The problem with this is if the head unit goes wrong (and they do), there is not a lot you can do apart from fixing it. You cannot nip down to the local car accessory shop and buy a new head unit, because you would have to re-wire the doors and boot.
Mine started switching off, then back on again, the display went dim, and eventually it stopped working all together.
So the option I chose was to get Clarion to repair the unit. They usually advertise on ebay, but you can also phone them direct on 01285 861 861. The process was really easy, you send them the unit, once they have received it, they phone you and tell you how much it will cost, you give them your debit card details, they repair the unit and send it back. The cost was £80 plus I also got them to add on an AUX cable for an extra £20. So for £100, I now have a refurbish head unit, they even put a new display on it and removed the code, so that I do not have to remember that anymore.
Once I got the head unit back, I drilled a hole in the base of the tray, to bring out the AUX cable, plugged everything back in and Bob's your Uncle, a working sound system again.
The AUX in works really well, just plug the MP3 player in and if the head unit is set to radio it automatically switched to the MP3 player - cool. So I think the 6 CD changer in the boot is rather redundant now...
I can heartily recommend Clarion, there customer service was very impressive, well done guys.