The springs & shocks from the S6 would fit the RS6 no problem as the mounting points are the same, as well as the control arms. The only difference would be if the spring rates are what you want. Here in N.A. we only got the S6 Avant so the H&R's here are for the Avante, not the Sedan. You could go with RS6 H&R springs with S6 shocks/struts, but why? If you want a non DRC suspension go with KW V3's or import a set of H&R coilovers.