An acquaintance did this on his W205 C63 and he reported that the car ran like crap. I was struggling to understand why, but then realised that the rear boxes are valved so perhaps the ECU was looking for them, yet couldn’t get an electronic or vacuum signal, consequently causing it to pull something back. I don’t have all of the facts but I wouldn’t expect the ECU to pull timing because of this, and generally removing any restriction on a turbocharged engine is beneficial and not subject to the same science as NA.
Maybe do some research into this if the E63 is similar.
Daveenty had Weistec down pipes, secondary cats and resonator removed on his 5.5 biturbo and it was very loud!
Alps put the resonator back when he bought it to calm it down a bit