So just to save you some legwork ... I am fairly certain the top secret items ColdList is talking about are parts developed by the German tuner Noelle . They are a great shop and have a very good reputation.
However they are in the same boat as any other tuner in regards to warranty / coverage , ie aftermarket.
They have a program for the M5 available at
http://www.noellemotors.de/en/produc...e-s63-tue.html
For their stage 2 and 3 you will also buy new downpipes and rear mufflers developed by Boyes who also do contract work for BMW.