THE S6 completes Audi's S-car line-up and slots in at the top rung of the A6 model range. What it lacks in visual differentiation over the A6 4.2 quattro, the S6 makes up for with uprated engine performance, improved dynamics and, perhaps most importantly for the prospective buyer, bucketloads of standard equipment including sat-nav and telephone. It's still not a match for the BMW M5, but this is the closest Audi's all-wheel drive A6 has come.