Not much is done basically, the MTM RS5 isn't a radical tweak as the 450bhp thereabouts 4.2 liter V8 makes.......450bhp. Yes, it is the same power output the RS5 had when it left the factory but the ECU is tweaked to allow the car to reach a maximum speed of 303km/h (188mph) instead of the usual German manufacturer limit of 250km/h (155mph). Audi does offer an increased speed limit too, but it is only to 280km/h (174mph). So this is a good thing if you intend to keep up with some 911GT3s or to actually boast a higher V-max than your other RS5 buddies at an Audi gathering.
The ECU tweak costs1499 plus 125 installation costs in Germany and the stainless steel exhaust will cost another 2999 and another 334 to fit it. It seems that this time we do know how much something from a tuner costs, which is good, as we actually now know how much we have to pay (especially that thousand over Euros just to increase the speed limit).
A more manic version is in the works. This is obvious as the mods are too subtle and too little, especially for a tuner like MTM.