Originally Posted by The X Men
BMW's valvetronic system is similar with Audi's Valvelift System, they are both basically varible valve system, invented by Honda years ago. The S6's cylinder deactivation works together with the Valvelift System to increase fuel efficency. Thats one of the reason why the S6 gets 17/27 MPG while the 550xi only get 16/24 MPG.
Watch out, the 650i Xdrive has more output and consumes less fuell, without cilinder shut down! S6=225g COČ and 650ix=215g COČ so the consumption is less with only Valvetronic. The 550i will get this update also this year so the lagging position is only temporal.
Audi's Valvelift is more VANOS+VTEC I guess and not a functional equivalent of valvetronic.