Now this stuff is way beyond my level of car knowledge but isn't the 535 a N55 engine and the 550 a N63? I guess I would assume for the 535 you'd buy the n55 tuner and for the 550 you'd buy the n63 tuner. Even on the Burger Tuning web site for the N63 it says "BMW N63 Eight Cylinder Turbo Motors"
2013 BMW 535i Xdrive, msport, Jet Black/Cinnamon Dakota leather (delivered 3/15/2013)
Current car: 2010 MB W212 Black/Black
Previous car: 2008 MB W211 Black/Black