Just bought a 2008 S4 after coming from many years in a Subaru WRX STi. I was interested in more information regarding Audi's Torsen system, and more specifically which of the diffs use it. Just for my education, what are the differences between the differentials running on my Audi - between the front wheels, between the rear wheels, and between the front and rear axles. FYI, the Suby was modified viscus, mechanical, and electro-magnetic, respectively. Thanks!