click link, scroll down and highlight section under the Red RS4<ul><li><a href="http://www.motorauthority.com/cars/audi/audi-improves-quattro-awd-with-new-sport-differential/">http://www.motorauthority.com/cars/audi/audi-improves-quattro-awd-with-new-sport-differential/</a</li></ul>

Sounds similar to a haldex system but different (ie.: not primarily FWD like that on the TT quattro)

<i>Audi has developed a new performance differential for its quattro AWD cars that'll be available from next year onwards. The new system distributes torque from the engine independently between the rear wheels, improving traction beyond that of the current AWD set-up. According to Audi, the tendency of its AWD cars to understeer has been reduced to almost nil thanks to the system analyzing acceleration, yaw angle and speed to identify where traction is lost.

In its basic setting, the torque-sensing centre differential delivers 40% of torque to the front axle and 60% to the rear. The new set-up is able to send part of this torque to the individual rear wheels almost instantly (less than 100 milliseconds) if it detects any loss of traction. The new differential features a multi-plate clutch running in an oil bath, with the clutches activated by an electro-hydraulic actuator.

Drivers will be able to select from three different operating modes, with `comfort' mode focusing on stability, `auto' mode providing a balance between stability and handling, and finally `dynamic,' which offers the best handling but the roughest ride. </i>

this quote "torque to the individual rear wheels" makes me think it could be a replacement just for the open rear diff and that they'd keep the torsen center diff. This is probably just the torque vectoring feature that's already been reported.

It's basically a rear LSD with a brain

The A5/S5 will get the Quattro Torque Vectoring (QTV) system when the B8 A4/S4 gets the QTV system at the beginning of MY2009.

Or, the A5/S5 will get the QTV system in the spring of 2008 for MY2008.