Inside, the differentiation between A6 and S6 is equally restrained. Gray birch trim, which can be replaced with optional carbon fiber inlays, dresses the dash, doors and center console, a three-spoke thickly-padded steering wheel replaces the four-spoke version found in the A6, and S6 nomenclature finds its way to the tachometer. Otherwise, the S6 and A6 are nearly identical, which means they both feature top-notch plastics and leather, as well as interior build quality that is among the best in the industry.