The AMG tune may be a bit more mild than the Renntech version but its quality is certainly top notch in any case. What kind of gains and other features does the AMG tune provide? I'd go for the AMG chip and the AMG airbox (I would assume a chip/airbox matched set tune would help that much more...) and skip the rear muffler all together. To get real gains you would need to do the whole exhaust system. Tuner exhausts are gawd-awful expensive. Since you have a 500E and want to tune the exhaust I'd get in with Lou N. and give his solution a try. You'd probably end up paying the same for a complete system that is tuner quality for what AMG/Renntech wants for just a cosmetic muffler. When it comes to ASR defeat, I might just try PAD. Just make sure it integrates with not only the stock parts, but the tuner gear as well. (can't think why it shouldn't, but there can always be annoying little "suprises" as complex as these cars are...)

Hope this helps...Lee

PS if you have a G-tech, some brass gonads, and some good/flat/deserted road you could order all 3 of the chips and test out which is the fastest. (then utilize the money back guarantee on the other two) We'd be happy to publish your results...