The S63TU is muffled by the turbos so opening up the exhaust makes a night and day difference in the sound quality and aggression. A simple way to achieve this goal is with muffler bypass pipes. They are cheaper than a full exhaust exhaust system and they simply bolt right on. At $1395 these are not 'cheap' bypass pipes but when compared in the context of F10 M5 exhaust systems the pipes become a value.
As all you are doing is really ditching the mufflers there is not much of a performance gain to be had but the bypass pipes are 14 pounds lighter than the OEM mufflers.
Check out the video below to get an idea of the sound quality. Combining these bypass pipes with a good set of downpipes will make a nice difference in the performance and sound quality of the F10 M5. Definitely something F10 M5 owners should look into to get more enjoyment from their cars.