The Good: The 2006 Audi S4's sophisticated V-8, mated to a solid six-speed manual, delivers steady power throughout its revs, while the Quattro system and associated electronics keep it on the road. And we like Audi's MMI controls for infotainment functions. The Bad: The Bluetooth interaction with our phone was surprisingly limited in the 2006 Audi S4. Ergonomically, the brake pedal was a little high, and the driver armrest interferes with the hand-brake lever. The Bottom Line: The 2006 Audi S4 commands a hefty premium over the standard A4, and although the cabin gadgets are similar, the performance gain is worth it. We had some minor issues, but overall, this is a top tech car. 2006 Audi S4The 2006 Audi S4 attempts to one-up the much-lauded BMW M3 by using the tried-and-true muscle-car practice of stuffing a larger car's V-8 under a smaller car's hood. The current M3 may squirt to 60mph a hair quicker than the S4, but the cachet, not to mention the sound, of the V-8 under its hood will probably make happy buyers out of some would-be M3 customers. Under the hood, technology such as dual overhead camshafts, variable valve timing, and five valves per cylinder help the 2006 Audi S4's V-8 churn out 340 horsepower. With Audi's stalwart Quattro system driving all four wheels, the S4 remains composed and predictable, and electronic stability controls keep the power from overwhelming the tires on loose surfaces.The face of the redesigned S4 features the signature Audi chrome-ringed grille, but the car is otherwise discreetly more masculine than the 2006 Audi A4 and pleasantly purposeful to behold. Sporting the bulging wheel arches of the new A4 but with rocker-panel cladding and a small rear spoiler, the S4 is different enough to be discernable but not showy. Our car's understated Light Silver Metallic paint ($475) fit the confident character of the styling; brighter colors will likely make the wide snout stand out more.With an MSRP of around $46,000 and our car's as-tested price at $56,045, the 2006 Audi S4 is substantially dearer than the V-6-equipped A4, starting at about $36,000 for a Quattro. But the difference is both outwardly visible, if subtly so, and palpable from the behind the wheel. The S4's combination of performance, style, and AWD controllability is well worth the upgrade.The 2006 Audi S4 impresses with its interior, as we've come to expect from all recent Audis. Materials are good quality, design is tasteful, and the layout and feel of both the mechanical and electronic controls are highly satisfying, with the exception of the hand-brake lever. Overall, it's a minor complaint, but the driver armrest sits over the lever, requiring the former to be lifted to move the latter. Immediately upon sitting in the bolstered Recaro sport seat and grasping the thick three-spoke steering wheel and leather-clad shifter, the driver anticipates an experience a step beyond that of the average sports sedan. The gauges are large and legible white on black, the speedo and tach separated with an information screen using Audi's usual red digital LED.We like the MMI control system on Audis, which forgoes trick features for functionality.The full-color main screen for the multimedia interface (MMI) is crisp, and the system's combination of a main control knob with four surrounding contextual buttons works much better than the iDrive in the 2006 BMW 750Li we recently tested. Audi Navigation Plus ($1,950) offers clear maps, relatively simple settings, control, and display of the next route step on the smaller screen between the main gauges. A row of hard buttons beneath the screen makes switching between the various infotainment systems quick and easy.Our car was spruced up with the Premium Package ($2,900): a glass sunroof; heated front seats; split spoke-design 18-inch wheels (different 18-inchers are standard); a HomeLink transmitter; autodimming mirrors inside and out; memory functions for seats and outside mirrors; a light- and rain-sensing system that turns on the headlights and adjusts intermittent wiper frequency; and adaptive headlights. Also checked on our car's options list was the Cold Weather Package ($400), featuring heated rear seats and a ski-sack pass-through from the trunk.A six-CD changer resides behind the glove-box door, an arrangement we like better than trunk-mounted changers for easy loading and unobtrusiveness. Our car came equipped with the Premium Audio Package ($1,500), which upgrades the standard Audi Symphony setup to a Bose system with surround sound and a dynamic noise-compensation feature. A microphone in the cabin regulates the stereo's volume in specific frequencies to compensate for unwanted interference, such as that from passing vehicles. The sound from this system is very refined and doesn't lend itself to pumping out bass to ridiculous levels.Who needs iPod connectivity when you can bring along a few gigabytes of music on SD cards and plug them directly into the sound system?The 2006 Audi S4's Premium Audio Package also includes preparation for either XM or Sirius Satellite Radio, controlled via the MMI or steering wheel buttons, as with the other audio features. Also part of the package is Bluetooth phone integration. The Motorola V551 we used for testing linked with the car easily, although interaction was limited to speakerphone usage--phone book information was not displayed, and the car offered no dialing system of its own.Our favorite of all the 2006 Audi S4's gadgetry is the SD-card reader in the dashboard. As we saw on the Audi A4, the MMI's screen tilts down and forward to reveal two slots to accept the portable media. MP3 files are read from the cards immediately, including title and artist information. We've been frustrated by the lack of MP3 player inputs for the higher-end factory audio systems we've tested of late, with a car's chance of having an auxiliary jack on the dash somehow inversely proportional to its sticker price. The ability to swap the same storage device from computer to car nicely obviates the need for the car to recognize and deal with a hardware go-between; you can just give the data to the car directly on an SD card. Music played this way sounded similar in quality to CDs or the satellite radio--Sirius, in our car's case. While the other occupants of the 2006 Audi S4 will enjoy the luxurious aspects of this car, the driver will understand the true nature of this beast. The S4 seems poised under any and all normal driving conditions, as well as some slightly abnormal ones. A feeling of utter solidity and the confidence of abundant power come together in this car, unlike with a few other four-doors. The component that puts the 2006 Audi S4 in a different league than the A4 is of course the motor. An all-aluminum, 90-degree V-8 displacing 4.2 liters, it feels smooth and eager throughout the rev range. With a two-stage intake manifold supplemented by variable timing on five valves per cylinder, the engine is perfectly suited to the chassis. It also sounds fantastic. Engine braking from 5,000rpm in second gear can become addictive. Replaying this soundtrack may negatively affect fuel consumption, which is already EPA rated at a low 15mpg in the city and 21mpg on the highway.This 4.2-liter V-8 is one big engine for a relatively small car, giving it power all through its revs.Some of our staff thought the 2006 Audi S4 felt slightly sluggish moving away from rest, as if the electronics that keep the tires gripping pavement prevented the car from pressing the driver into its seat, but none complained about a lack of power otherwise. Revving to 4,000rpm and dumping the clutch would be a sure way to avoid sluggishness, and despite the antisocial implications of such unrecommended antics, this drivetrain feels as if it would barely notice.The 2006 Audi S4's aluminum suspension is sprung and damped more tightly than the regular A4 setup. Handling is precise, thanks to Audi's Quattro all-wheel drive, and electronic systems work to keep the S4 on its intended path. The electronic stabilization program incorporates the antilock brakes with electronic brake-force distribution (EBD), the electronic differential lock, and antislip regulation to slow individual wheels when diversion from the intended path is detected. The S4's adhesion limits are high enough that ESP won't be noticed unless the car is really pushed. Even with a run on a twisty and freshly wet road at speeds that might have triggered it, we were never aware of the system intruding.Six choices on the manual gear shift gives drivers a lot to work with.We were pleased that our car came with the standard six-speed manual transmission. Weight savings of 75 pounds aside, the direct feel and involvement of this particular gearbox is extremely satisfying. Together with Servotronic speed-sensitive steering and the engine's reserves of midrange punch, the effort level of the controls complement each other to make this 4,000-pound car feel both tossable and totally safe.Our only minor complaint about the 2006 Audi S4's driving experience was the height of the brake pedal in relation to the other two pedals. The clutch effort is just enough to feel direct without tiring the leg, and the brake pedal likes a comfortable shove and allows easy modulation. But the brake felt closer to the driver than we wanted, and more than once, we caught our shoe on the side of the pedal while transferring from the accelerator. Fans of heel-and-toeing will need to spend some time practicing in this car--or we need to do some Achilles' stretching.The road-holding ability of the 2006 Audi S4's Quattro all-wheel-drive system might be said to be its most apparent safety feature, but dedicated systems are ready, should something go wrong. In addition to all the chassis-control wizardry, a number of acronymless features help the S4 further protect its occupants. The expected dual-stage, dual-threshold front air bags are in place, with occupant sensors. Side-impact air bags are integrated into the front seats. Separately, the Sideguard curtain air bags protect the heads of front and rear occupants. Active head restraints on the front seats are standard.As mentioned earlier, the 2006 Audi S4's brakes are controlled with ABS and EBD. Also present is a disk-wiping feature that uses occasional soft caliper pressure when driving on wet roads, so the disks will be free of any built-up moisture if immediate stopping power is needed.Adaptive headlights point into corners to keep the road illuminated. A headlight-washer system, flush to the bumper when not in use, keeps the lenses clean.Audi's new-vehicle warranty protection is for 4 years\/50,000 miles, extending to 12 years for corrosion perforation. During the main warranty period, scheduled maintenance is covered by Audi, and 4-year roadside assistance is also included.