Most folks disconnect or code out the center speaker. I did the latter in my car. I have the same Audiotech-Fischer amp. I've also replaced the front speakers with Eton (my car has the HK option). The rears were replaced with JLs. The real change came when I added the Audiotec-Fischer USB module to the amp. This bypasses the head unit's digital to analog converters. Basically, I had to run a 15' USB cable from the center console to the USB module in the amp. Then , I had to tell the amp that a signal on he USB cable has priority over the analog signal from the head unit. OMG! Difference was day and night!
https://www.audiotec-fischer.de/en/m...p-7bmw/up-7dsp