I have the 6 disk changers removed from both my wife's 2002 530i, and my 2004 X5 for sale. Both are complete and fully functional, with magazines, look almost new, are made for BMW by Alpine, include the DSP output connector, and are compatible with any i-Bus equipped BMW. In other words, they will work in nearly any I-bus compatible BMW made since '97, with or without DSP (excluding the latest Banglized disasters from Dingolfing.)
The one pulled from my X5 is BMW part number: 82111469404, Dated Nov 2003. It's been used from new until Nov. 2006, when it was replaced by a DICE Ipod adapter. Price $175 + shipping.
The one pulled from the 530i is BMW part number: 65126913388, Dated May 2002. It's been used from new until Dec. 2007, when it was replaced by a DICE Ipod adapter. Price $150 + shipping.
They are interchangable, and will both work in an M5, or any E39, E38, E46, E53, etc . . . . The difference in price is just due to the different amount of usage and age. Local pickup in Ventura County CA, near LA is also welcome. PM me.