Personally, I don't think its styling is adequate. It's too niche, not prestige enough to be an executive sedan. In the smaller A4, niche could be its advantage, but in higher class this trick might not work. On the contrary, the interior looks every bit of very high quality and taste.  

So now Audi has made the A6 a bigger A4, placing it above the A4 in size and above Volks Passat in quality. However, is it good enough to beat the class-leading BMW 5 series? I don't think so. As Autocar's test has found out, no matter steering feel and body control, A6 is less brilliant than the 5 series and Mercedes E280 V6. Obviously, A6 is not as dynamic as both of its German rivals. However, superior build quality combines with competitive pricing, especially the 2.4 version, means Audi A6 represents great value. 
 

A6 Avant 2.7T Quattro

You may remember that a similar engine, but with 265hp and 295lbft, has been installed into S4. In A6 Avant turbo, the output is lowered to 230hp and 228lbft because the Tiptronic gearbox (which is a must for this kind of car) cannot cope with so much torque. Anyway, A6 still tops 151mph and manage 0-60mph in 7.3sec, very good for a car weighing nearly 1700kg.  

Handling conforms to the same character as engine : its Quattro 4-wheel drive system provides first rate security and full confidence to use in any slippery surface, though accompany with understeering that tells you this is not a really exciting sports wagon. Then, Audi's traditional lifeless steering again reminds you this is a luxurious wagon with good performance, rather than a high performance wagon with good luxury.  

At the end, considering the dramatical price hike over the normal A6 Avant 2.8, I don't think the turbo Quattro behaves good enough to justify the cost. It is something between a practical wagon and a sport wagon, but hardly please the customers of both sides. 
 

A6 V8

The heart and soul of the car is the all alloy V8 carried over from A8, which has been upgraded with 5-valves head, 3-stage variable induction and variable valve timing. For unknown reason, it delivers slightly less punch than the A8, although 300hp and 295lbft are still respectable. Without surprise, the high power A6 comes with compulsory Quattro drivetrain plus the 5-speed Tiptronic with steering-wheel control.  

Obviously, changes go deeper than the engine bay, otherwise it would be impossible to reverse the unfavourable reputation about handling. As in the facelifted A8, suspension links are now made of aluminium in order to reduce unsprung weight, thus benefit ride comfort. Another predictable change is the stiffening of springs and dampers, because : 1) the increase of kerb weight requires it; 2) the reduction of upsprung weight allows it. 3) car lovers want it. 

Other changes are rather minor, such as adopting 16in 235 tyres, widened front track and fenders, aluminium bonnet, restyled grille... The A6 4.2 really looks more muscular. Now we're going to see if it performs as well on road...

On highway, A6 4.2 goes fast and smooth with very high directional stability. However, carrying a kerb weight of 1730kg against 540i's 1660kg, it takes an extra 0.5 sec to 60mph. Contrary to this is the weighting of steering, which is in Audi-tradition's lightness. The Quattro also places practicality over driving excitement by understeer all the way in corner. You can't access throttle oversteer like the rear-wheel-drive 5 Series. In return, it generates superior grip in snow or wet surface that any stability control can never keep up with. 

It seems that once again the Audi is designed with Autobahn cruising in first priority. Once ride on rough road, its body control deteriorates. It feels quite bulky compare with 540i, thanks to the kerb weight, the quattro and, perhaps more important, the inferior suspension tuning. Considering its four links / double wishbones setup, Ingolstadt has no excuse to be inferior. The same is for the ride, even in the standard tyres, it can't match the effectiveness of bump absorption of the 540i in sports suspension package. 

If there were any excuse, it must be the fact that its chassis was developed from A4 and Passat, and will be shared with the forthcoming Passat Plus. Nevertheless, A6 4.2 is no cheaper than the similarly equipped 540i, what a pity. 

Before ending this report, a question must be raised : buy an A6 4.2 or an A8 4.2 ? Some magazines said the A6 is more bargain, but I'd rather choose the latter. Ridiculously, the A8 is actually lighter than its little sister, thanks to ASF, so performance is at least as good. Previous comment about the A8 with sports suspension is favourable (See A8 section). Of course it cost considerably more, but in return you'll get a really luxurious yet more exciting big car. 
 

Audi S6

At last, Ingolstadt plugged the last piece of puzzle into the S series sports sedan range - S3, S4, S8 and now comes the S6. Technically speaking, S6 is not interesting enough for me to write more than 200 words, since it is essentially a combination of A6 V8's chassis and the engine of S8.

Like the A6 V8, the structure at the front has been widened and strengthened for accommodating the V8. The secondary grille at the bumper is also the same as the V8, but at either side there is an additional intake for cooling brakes. However, the most distinctive features are the 17-in Avus wheels wearing 255/40ZR17 tyres, and then a pair of polished side mirror and a black stripe running at the lower edge of the doors. 

Underneath the skin may see more deviations. Firstly, the 4.2-litre V8 has been upgraded to S8-spec although marketing strategy calls for a reduction of 20hp. In other words, it is basically the standard 40-valve V8 using by the A6 V8 and A8 but with the following modifications : 1) revised induction manifolds. Instead of 3-stage variable length, it chose a simpler 2-stage design with higher flow rate; 2) sportier cam profile; 3) revised exhaust with lower back pressure. As a result, the V8 output 340hp and 310 lbft instead of 300hp and 295 lbft.  

Although the front and rear subframes are now made of aluminium instead of steel, manufacturer's figures say the S6 weighs as much as 1790kg, which is 60kg in excess of the A6 V8, or nearly 40kg heavier than the already overweight BMW M5. Considering the power and torque of the lightly revised engine, the S6 can hardly keep pace with the 400hp M5, the 370hp Jaguar XJR and the 391 lbft Mercedes E55 in terms of speed. Audi claimed it could sprint to 62 mph in 5.7 sec, or around 5.5 sec for 60 mph, but I believe 6 seconds is more realistic. For Tiptronic model, it could be even slower. 

Unlike the A6 V8, this car provides a 6-speed manual in addition to the 5-speed Tiptronic S. Another attempt to tighten the handling is the reduction of steering ratio to achieve a 2.5-turns lock-to-lock. Besides, the suspensions get firmer setting while ride weight is lowered slightly by 10mm. As usual, Quattro system is compulsory because the standard A6 is a front-wheel-driver. Naturally it split 47 : 53 torque between front and rear axle. At the most critical circumstances the Torsen center LSD partially locks up and transfers at most 70% to either axle. 

How does it drive ? like other big Audi (A6 V8, A8 and S8), it is a born Autobahner. Quick and smooth, with remarkable high speed stability. Grip is always tremendous so that the electronic stability program (ESP), electronic differential lock (EDL) and traction control (ASR) are rarely used. Ride is quite good on highway. Brakes are always effective to stop the 155mph car. The revision in steering sharpen turn-in response yet increase feedback from the road, this makes the S6 more satisfying to drive than the A6 V8. However, on twisty roads it doesn't display the level of involvement and adjustability as BMW M5. Ride quality also get worse there. And the power deficit is obvious when compare with its rivals.  

The cabin looks very sporty. Recaro sports seats aside, the interior is trimmed by Alcantara and carbon fiber. However, is the S6 really that sporty ?