Just my opinion, but that’s probably because the S6 was kinda’ “lame” in Europe, we had the RS6, so people who wanted refinement, went for S8, and ones who wanted sport-sedan/wagon took the RS6, leaving the short stick to the S6. Because the C6 RS6 was not imported to N-A, S6/S8 were the only contenders there. Thus more widely sold and known. Still, I like the understated looks and N/A sound and feel of the C6 S6 over the bi-turbo C6 RS6… although when built correctly that car can be insanely … insane:
https://www.google.com/url?sa=t&source=web&rct=j&url=https://m.youtube.com/watch%3Fv%3DNIqrs-ZSiAk&ved=2ahUKEwi9u6Ooy5PoAhVtwosKHbprA0UQwqsBMAB6BAgGEAQ&usg=AOvVaw23wajOMfSqGFrjDrLLim5Q
Cheers,
Kristjan