Audi’s new A6 model series will soon welcome a new member into the family, the sporty S6 that was snagged by our spy photographers in Avant trim during testing in Germany.

The prototype model was completely undisguised, however, there’s a reason for that. With the exception of some model specific details such as the telling quad tail pipes and unique alloy wheel designs, the S6 will remain unchanged from the A6 with the optional S-Line sport package. The latter adds an aero kit with restyled front and rear bumpers, among other parts.

Both the S6 sedan and Avant models will also get the S-Line interior treatment with standard sport seats and optional bucket seats up front, a flat-bottomed steering wheel and different trim decorations.

What makes the S6 stand out from the regular A6 models is well hidden under the bonnet: the new S6 will pack the Volkswagen Group’s newly developed 4.0-liter V8 engine, which will be used in a variety of high-end cars including the entry-level models of the Bentley Continental series.

The eight-cylinder lump is believed to make around 450-horses, which will be channeled to all four wheels through a seven-speed dual clutch transmission and of course, Audi’s quattro system.

The S6 is expected to be unveiled before the end of the year and reach showrooms in the first half of 2012.

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