I had a set from Vizualogic in my E60. Worked well, but the problem is that they match the leather to the general 5 series and not the M5. I also think that ther may be some head restraint fucntion played by the stock headrest, so I would want to confirm that, if there is, it isn;t affected by the swap out.
What about aomething like this:
http://www.turnermotorsport.com/p-16...FStk7AodAkUAHA