They're not coilovers but I just installed Koni FSD dampers on my S6 with the stock springs and I'm pretty impressed so far. It's "soft" feeling while driving normally but they handle body roll and pitch impressively. They're actually pretty strange feeling because you don't get the confidence from a really "firm" ride, but they definitely work well when needed. It's kind of hard to explain. We use the S6 as the everyday family vehicle so the FSDs are perfect for that use. If you're looking for a smooth ride, they're worth checking out.

edit: I have to agree about the DRC. My RS6's DRC is still intact and functioning and the ride is absolutely perfect. Just the right amount of firmness and almost no body roll.