A sedan with a V10? That's got to be awesome, right? What if we said that V10 came from a Lamborghini? "Wow," you'd say. "What is this amazing car?" Well, it's the 2010 Audi S6, but as it shakes out, sometimes things that sound amazing don't live up to the hype.

For starters, the S6's 5.2-liter V10 is indeed sourced from the Lamborghini Gallardo; however, it has 127 horsepower less than the Lambo and 100 hp less than the Audi R8 V10, which also uses a variation of the same engine. More importantly, the S6's 435 hp is 65 down on the V10-powered BMW M5 and 83 down on the new Mercedes E63 AMG. The result is a sedan that gets thumped in a straight line by its competition and one that barely edges out its plebeian A6 3.0T sibling.

The S6's issues don't end there. Because 59 percent of its weight hangs over the front wheels, even its Quattro all-wheel-drive system's 40/60 power distribution can't save it from speed-scrubbing understeer. In other words, it's got significant handling disadvantages as well. You'd hope that it would at least have a comfortable ride, but no luck there, either. The standard 19-inch wheels and sport suspension produce a bone-jarring ride, when the E63 and Jaguar's 510-hp XFR manage to handle well and cosset their passengers' backsides at the same time. On the upside, 18-inch wheels are a no-cost option for those who'd prefer a comfier ride, and the standard brakes provide ample stopping power.

This relative damning of the S6 should be weathered by the fact that it certainly is not a bad car. It's still powerful, still stylish, still remarkably luxurious and still crammed with useful high-tech electronics. It's also $10,000 cheaper than its fellow German super sedans and $3,000 less dear than the XFR. However, if you're looking for the best super sedan in this price ballpark, the S6 is simply outdone by every competitor, including the rip-roaring Cadillac CTS-V ($20,000 cheaper) and Audi's own S4 ($30,000 cheaper). It's hard to comprehend a sedan with a Lamborghini V10 not being drool-worthy, but the 2010 Audi S6 proves it's possible.

The 2010 Audi S6 is a high-performance sedan available in one loaded trim level. Standard equipment includes 19-inch wheels, summer tires, a sunroof, adaptive xenon headlights, LED running lights, front and rear foglights, keyless ignition/entry, power tilt-telescoping steering column, eight-way power front seats with lumbar adjustment and driver memory functions, leather upholstery, heated front and rear seats, a rearview camera, Bluetooth, the MMI controller, a hard-drive-based navigation system (includes real-time traffic) and a 13-speaker surround-sound system with six-CD changer, satellite radio and iPod interface. Options include rear side airbags, non sport seats, a blind-spot warning system and 18-inch wheels with summer tires.

The all-wheel-drive Audi S6 is powered by a 5.2-liter V10 that cranks out 435 hp and 398 lb-ft of torque. A six-speed automatic with manual shift control is the only available transmission. At our test track, the S6 ran from zero to 60 mph in 5.7 seconds -- barely quicker than the A6 3.0T and woefully slower than the BMW M5, Jaguar XFR and Mercedes E63. Fuel economy estimates are 14 mpg city/19 mpg highway and 16 mpg combined.

Standard safety equipment on the 2010 Audi S6 includes antilock disc brakes, stability control, all-wheel drive, front-seat side airbags and full-length side curtain airbags. Rear side airbags are an option. In crash tests by the Insurance Institute for Highway Safety, the Audi A6 (on which the S6 is based) scored the highest possible rating of "Good" in both frontal-offset and side-impact tests. In brake testing, the S6 came to a stop in a fade-free 110 feet -- a good result for this type of car.

The 2010 Audi S6 handles well for a nose-heavy 4,500-pound AWD sedan, but it simply can't keep up with the quicker and better-balanced competition when the going gets curvy. There's no payoff in terms of ride comfort, either -- the S6's suspension is sports-car stiff. As good as the V10 sounds, it doesn't produce the thrust needed for the S6 to be competitive in this rarefied high-performance segment, and the six-speed automatic isn't as responsive as the dual-clutch automated manual gearbox found in the Audi S4. Braking, it seems, is about the only thing the S6 unequivocally excels at.

Trimmed in leather and aluminum with birch wood accents, the S6's cabin carries on the Audi tradition of finely wrought interiors. The amply bolstered front sport seats provide good support during aggressive driving, though if you dislike that hugged feeling, the A6's normal seats are a no-cost option. Interior room is spacious, with plenty of room for four passengers to travel in long-distance comfort. The trunk offers 16 cubic feet of space, which is pretty good for this size of car.

The S6 comes with Audi's latest Multi Media Interface (MMI) vehicle management system, which controls entertainment, communication and optional navigation functions via the dash-mounted LCD screen and center console-mounted controls (a knob and buttons). Though there is still a bit of a learning curve involved in using it, MMI has been dramatically improved for 2010 -- especially in regards to navigation functionality.