What year is the S6? Is this Avus silver or light silver metallic?
I have an A6 and S6 avant, both in Light Silver Metallic. Dodo Juice diamond white and/or light fantastic look great on them for wax.
For a sealant, Blackfire wet diamond and Menzerna Power Lock both look great.
Finish Kare 425 is the best looking quick detailer I've used on Silver. Meguiars M34 is another good choice for a quick detailer.
Duragloss Aquawax if your in a cold climate and need a spray sealant to boost your protection during winter, but I don't think it looks as good on silver as the other things I mentioned.
Ultima Waterless Wash plus was the best looking of the "dry wash" products I've tried. It looks very nice on Silver.
If your S6 is a 2002 or 2003 light silver metallic, the paint is very hard. The menzerna line has worked well for my cars: SF-4500 + green, white or black lake country pad would be good combos to get the most out of the finish, this would be best achieved with a rotary.