We know this because we had a call from Kim Collins, owner of tuning outfit 'qst', the sole UK distributor of MTM performance products. He has already had 27 customers uprate their RS6s, and wondered if we'd like to try the 536bhp MTM factory demonstrator to see why they'd done it.

To understand why anyone would want to upgrade the ultra-rapid RS6, you have to get a handle on the lifestyle of the seriously rich, as these are the only folk likely to be able to afford to modify Audi's finest. These people want the performance of a Ferrari but tend not to be into showing-off. The 'stealth' aspect of the RS6 suits them perfectly and if they can make their estate car as brisk as a Prancing Horse, so much the better. Paying for the conversion isn't an issue, which is just as well, as you'll find out in a moment.

Using the MTM options list, you can choose just how mad you want to go. Base camp in the MTM power stakes is a revised engine management system liberating an extra 49bhp, bringing the total tally close to the 500bhp mark. Reaching this stage costs ΂£2115.

Next on the 'to do' list is change the exhaust from the downpipes back. This costs a further ΂£3407 and liberates an extra 12bhp. It does this via a clever butterfly valve within the pipes that opens up once boost goes over 0.8bar (max boost is 1.31bar) effectively creating a straight-through exhaust. It makes an astonishing sound.

The final stage of engine tuning involves swapping the exhaust manifolds and cats, which means the engine has to come out; the twin turbo V8 is so tightly stuffed into the bay there's no room left to work around it. So the extra 31 horses this change releases are the most difficult to corral and cost an additional ΂£4700, bringing the total spent so far to ΂£10,222.

The gearbox is also tweaked by a simple reprogramming of the gearbox computer, enabling it to cope with the increase in torque. It does this by stopping the 'box changing down quite so often in 'kickdown' mode and letting the massive torque do the work instead.

The expense continues outside the engine bay. The demo car has non-reclining Recaro buckets costing ΂£2820 the pair. The wheels are an MTM design, 9.5J by 19in fitted with 275/30 ZR19 Pirelli P Zeros, cost unknown as yet but expect no change from ΂£3000 just for the wheels. Hiding inside the front wheels are new 380mm discs; ΂£2174.
Although the springs and dampers haven't been replaced, all four spring platforms have been altered, dropping the ride height 15mm.

After that little lot has been added you won't be surprised to hear the RS6 is a very different car to drive. Nothing prepares you for the violent way 531lb ft of torque wrenches the Audi away from standstill. Then there's the unforgettably ballistic punch of the first dose of boost, and the incredible wall of sound generated by that trick exhaust.

It's loud enough to bring people out of nearby houses to see what's going on (it happened, really, during our test). The quality of the noise is pure Nascar and nothing like any turbo car I've ever experienced. But it's perhaps a little too loud; good job it's not a mandatory part of the spec.

The brakes, meanwhile, are superb - if a little too vocal around town, something a pad change might eliminate - and are definitely worth further investigation.

The increase in power offered by the MTM conversion is massively addictive, with a noticeable swelling in mid-range torque from what was already a very healthy total. Stage one of the modification package is certainly worth a look, but beyond that I reckon that the unique, stealthy attitude of the standard RS6, the thing that makes it so appealing, seems to get eroded with each additional tweak. If you can live with that (and how hard could it be?) you certainly won't be disappointed. After all, you can't take the money with you.