MONTREAL – Despite the heart of a raging bull, Audi AG’s latest sport sedan, the S8, stands as the epitome of subdued excellence.

New for ’07 in second-generation guise, the S8 is the high-performance variant of the auto maker’s short-wheelbase A8 flagship. However, in place of the standard A8’s 4.2L DOHC V-8 or 6L DOHC W-12 sits a snarling longitudinal 5.2L V-10 sourced from the Lamborghini Gallardo sports car.

Audi purchased Sant’ Agata, Italy-based Automobili Lamborghini SpA in 1998 and has since revitalized the hallowed sports car maker with fresh designs and improved quality and technology.

In the greater scheme of things, the S8, on-hand at a recent Audi media event here, occupies a rarefied field. It is one of only a handful of large luxury barges to be outfitted for aggressive driving.

But outright performance is not the S8’s forte. It’s not brash enough to outgun an AMG-Mercedes-Benz S-Class from a standstill, nor is it exclusive enough to one-up a Bentley Continental Flying Spur at the local valet.

What the S8 offers is reserved style and performance – and loads of it.

And at $94,420 (including destination and gas-guzzler taxes), it will hold a significant cost advantage over its $100,000-plus rivals when it goes on sale in the U.S. in mid-November.

Garnished with moderate exterior changes, including a more aggressive front fascia, an S-specific, chrome-accented grille and integrated rear spoiler, the only real clues to the S8’s hidden muscle are its four oval exhaust outlets, a few discreet V-10 badges and unique 20-in., 7-spoke alloy wheels.

Monstrous 15-in. (38.1 cm) front brakes (13.2-in. [33.5 cm] units in the rear) and caliper blocks painted black with embossed S8 logos indicate prodigious stopping power from the 155-mph (249 km/h) electronically limited top speed, but are otherwise lost in the muted presence of the S8’s design.

The all-aluminum, 5.2L DOHC V-10 has been enlarged from the Gallardo’s 5L displacement to muster better low-end torque and drivability for the larger, heavier S8. Enhanced with Audi’s FSI direct-injection gasoline technology, variable valve timing and variable length intake runners, the compact V-10 produces 450 hp and 398 lb.-ft. (540 Nm) of torque, 90% of which is available from 2,300 rpm.

The Gallardo’s 5L V-10 produces 512 hp and 376 lb.-ft. (510 Nm) of torque.

Awakening the Italian beast under the hood evokes a subdued, yet throaty exhaust note that is instantly recognizable as coming from an odd-firing 10-cyl. layout.

Under acceleration, the engine emits a warbling crescendo of mechanical melodies all the way to its 7,000-rpm power peak.

On the road, where the standard quattro all-wheel drive and refined 6-speed Tiptronic automatic transmission (with steering column-mounted paddle shifters and rev-matching downshift capability) come into play, the 4,586-lb. (2,080-kg) S8 can dash to 60 mph (97 km/h) in 4.9 seconds, Audi says.

Although not frighteningly quick, acceleration is linear, with big, smooth doses of shove coming with each gear change.

Track-ready the S8 is not, but its revised 4-link front/trapezoidal-link rear suspension with adaptive dampers does a commendable job of making the executive limousine feel much smaller than it is.

The driver-adjustable air suspension sits 0.8 ins. (20 mm) lower than the standard A8, with the softest setting being equivalent to the standard model’s firmest sport setting, the auto maker says.

Once out of the city, the S8 attacks twisty mountain roads with little drama, gliding over all but the largest potholes while maintaining considerable poise and comfort. Steering is direct and responsive (10% quicker than the A8) with good turn-in feel. However, on-center tracking is rather vague at steady highway speeds, and the front seats could use more lateral support in corners.

Understeer in tight bends is expected from any AWD vehicle with a big engine hanging partly over its front axle. However, Audi’s new quattro system with a 40-60 front-rear torque split offers up a slight rear-drive bias that makes the S8 feel surprisingly playful at moderately aggressive speeds.

But the S8 is not designed to be the rush-hour racer or the boulevard extrovert. It’s aimed at those who appreciate – and maybe more than occasionally exploit – impressive performance and overall vehicle engineering, but who don’t care if anyone else notices.

Around town, the S8 effortlessly sheds its machismo and slips around with the utmost elegance and refinement.

Taking the already exquisite A8 interior to new levels, the cockpit of the S8 is highlighted by a fat, S-specific steering wheel, Alcantara headliner, aluminum accents, dark Birch Grey wood (carbon fiber is a $550 option) and an optional full leather upgrade with 2-tone, premium leather seats ($3,900).

The highlight of the interior is the audiophile-grade, 1,000-watt Bang & Olufsen stereo, a $6,300 option for which Audi is experiencing a near-100% take rate on initial S8 orders, says Filip Brabec, general manager-product planning.

With 14 speakers powered by individual amplifiers, noise-canceling digital signal processing and Acoustic Lens tweeters that automatically rise from the dash, the system’s volume and sound quality are simply incredible, rivaling some of the best high-end home-theater systems.

Other notables include standard electronic stability control and navigation with Audi’s Multi-Media Interface, eight airbags, active head restraints, light-emitting diode (LED) daytime running lights, advanced xenon headlights with adaptive corning lights and optional adaptive cruise control ($2,100).

For those on a budget, Audi offers the midsize S6 sedan, also in second-generation form, for about $20,000 less than the S8.

Sporting a detuned, 435-hp version of the 5.2L V-10, along with nearly the same drivetrain, suspension and features as the S8, the S6 helps grow Audi’s line of special S and RS models, while offering a slightly smaller and more nimble overall package.

Most of the S8’s interior and exterior design cues can be found on the S6. But the overall feel of the S6 is almost too subtle to be considered special.

Unique features to the S6 include 19-in., split 5-spoke wheels, as well as new sport seats that are supportive but a little firm on the backside. And, in symbolizing its 10-cyl. power, the daytime running lamps consist of five white LEDs on each side of the grille, arrayed horizontally.

Dynamically, the S6 and S8 are nearly identical, with the S6’s 0-60 mph (97 km/h) time coming in at 5.1 seconds, Audi says.

Chalk up the S8’s slight advantage to its aluminum spaceframe, which keeps the larger car’s weight to a minimum and lowers its center of gravity. A better power-to-weight ratio (10.2 lbs per hp vs. 10.3 for the S6) and shorter final drive gearing also help.

Running both cars back-to-back reveals the S6 is slightly more agile in most situations but lacks the overall stability of its larger brother. Throttle response also is not as sharp, and the steering is much more vague, especially on-center.

City/highway fuel economy for both cars is rated at 15 mpg (15.7 L/100 km) city and 21 mpg (11.2 L/100 km) highway, with real-world averages falling in the middle of the range after several hundred miles of fairly aggressive driving.

The S6, which also goes on sale in the U.S. in mid-November (base price $74,020, including destination and gas-guzzler charges), is available with many of the same options as the S8 and currently represents the top of the A6 lineup.

That is, until the second-generation RS6 debuts later in the decade packing a V-10 with some extra assist from twin turbochargers.

Johan de Nysschen, Audi of America Inc. executive vice president, declines to confirm details or a timetable for the RS6 super sedan, but he says current development mules are reliably producing up to 700 hp.

msutton@wardsauto.com