Hi Will,
I'm looking to do this as a B7 RS4 upgrade. I have sourced the rears but I am struggling to find the front discs and calipers.
As far as I know the upgrade can be done but some modifcation of the hubs is required.
I have the car booked in for the work to be done so I'll post some pics and a procedure with any problems encountered when its complete.
It may be in two parts if I can't source the fronts in time at a reasonable price!
Steve