I'd say it will depend on your dealer. The dealers I've worked with generally will not make a fuss about an aftermarket exhaust or intake, for instance - but not all are the same way. Best advice is talk to your SA about it.
That said, I have the MPE (port-installed) and it sounds great. Cat-back on an N55 (single pipe) probably won't do much better, and you run the risk of "highway drone", which can be very annoying.
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2015 F80 ///M3 Sedan 7DCT Tanzanite, 2022 X3 sDrive30i 8AT Brooklyn Grey
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