- Excellent traction courtesy of all-wheel-drive

- Much more enjoyable to drive than the standard A6

- Less expensive than its rivals

- All the latest safety features

- Lack of manual transmission limits driver involvement

- Lousy fuel economy

- To truly use all that technology you've paid for, you need a racetrack

Please pay attention, because this gets complicated. Audi’s sedan range consists of A-cars in four sizes: A3, A4, A6, and A8. The S3, S4, S6, and S8 are faster, sportier versions. Even quicker, more focused vehicles devised by subsidiary Quattro GmbH are designated RS.

The previous-generation S6 had a V-8 engine developing 340 horsepower. The twin-turbo RS 6 started life with 450 horsepower and ended up with 480. In the interim, Audi complicated things by endowing the smaller S4 with the 340-hp, 4.2-liter V-8 and the RS 4 with a direct-injection V-8 that makes 420 horsepower. The 2005 Tokyo show saw the debut of the S8, with a Lamborghini-derived V-10 and 450 horsepower.

All of this made us wonder how the new S6 would be positioned. After all, it has to upstage the S4 but stay below the S8 in the corporate pecking order. At the Detroit show in January, we found out. The S6 has the S8’s 5.2-liter V-10, but with its maximum output reduced by 15 horsepower to 435. And, yes, there will be a new RS 6, which is more than a year away and promises to outgun the 500-hp BMW M5.

Audi will tell you this is all logical, that each model has a specific purpose and its own niche in the market. In the case of the S6, Audi maintains it is not just another contender in the German horsepower race. It’s intended as a fast touring car rather than an out-and-out road racer and is purposely understated so it looks hardly any different from the A6.

The S6 certainly avoids the visual excess of some super-powerful sedans. There is little outward differentiation from the A6: bright vertical struts for the deep single-frame grille, flared wheel arches and rocker panels, special 19-inch wheels, and daytime running lights consisting of two rows of LEDs under the front bumper. Audi would have you know that there are 10 LEDs in total, corresponding to the engine’s cylinders, although the discreet V-10 badges on the car’s flanks are another reminder.

There is also nothing intimidating about driving the S6. The engine, which makes a strong, gutsy noise and should propel the car to 60 mph in 4.8 seconds, is docile when you want it to be; the six-speed Tiptronic automatic transmission works easily, whether controlled by the steering-wheel paddles or left to its own devices.

Like all Audi high-performance cars, the S6 has four-wheel drive. After years of promoting the even front-to-rear torque split of the Quattro system, Audi has given the S6 (and the S8 and latest RS 4) a 40/60 rear-biased distribution. This attempt to match the handling characteristics of its rear-drive rivals works — to a point. In a session on a tight, twisty test track, the S6 proved more agile than its predecessor but still felt front-heavy and understeered when being hustled hard; that’s not surprising, really, because that’s a big engine nestled between the headlights. On public roads in Germany, slick from recent rain, we were reminded, however, of the security provided by four-wheel drive in a powerful car.

Hot on the heels of BMW bringing the first V10-powered luxury sedan to the U.S. market – the 500-hp M5 – in 2005, Audi brings its own 10-cylinder contender with the 2007 S6.

The S6 is basically a high-performance variant of Audi's midsize A6 sedan. Using a less potent versoin of the V10 in the previously announced S8, the S6’s 5.2-liter engine produces 420 hp at 6,800 rpm and 398 pound-feet of torque. That's 70 hp shy of BMW's M5 engine, but Audi promises more of a bias towards luxury. Audi says the S6 will sprint to 62 miles per hour from a standstill in 5.2 seconds.

A six-speed automatic is the only transmission available. Quattro all-wheel drive comes standard, with a 40/60 front to rear torque split that enables a combination of rear-wheel drive dynamics (preferred by enthusiasts) and all-weather security.

Audi will also offer an S6 Avant wagon. Audi says it will hit 62 mph in 5.3 seconds, which would make the Avant the quickest wagon sold in North America. Sedan and wagon versions of the S6 will go on sale this spring, while the larger S8 is set to arrive in the fall.