For more on the current model, including pricing with options, see our full review of the 2013 Audi A6 and S6. The Audi A6 is a mid-size luxury four-door sedan that's been on sale in America since 1995. Eventually joined by a high-performance S6 sedan, the A6 has been Audi's challenger for the Mercedes-Benz E-Class and the BMW 5-Series. With the...