I've got an ms-8 installed in my shaker1000 car. I cut the leads comming out of the back of the stock head unit to connect the inputs of the ms-8. I also connected the sub output that went to the shaker1000 subs to the ms-8 inputs. I ran new speaker wire to the doors because I'm running a 3way front stage consisting of alpine spx-13pro component set and a dayton rs225 8" midbase driven by a JL audio 600/6 6 channel amp. If I was to do it again I would have tied back into the factory wiring going into the doors since there is 3 pairs of speaker wire already for the 5x7 and the dual voice coils of the door subs. I feed the factory shaker1000 subs and amp from the ms-8.
For me the main advantage of the ms-8 over other processors is the automated tuning and versatility of the crossovers.
After reading a lot about ms-8 installs on 12volt.com and problems people were having with echo during Bluetooth phone calls I decided to connect the system to the rear outputs of the head unit. Then I connected the front outputs of the head unit to factory rear channel amps and speakers. On the head unit I have the fader set to rear. This way music plays through the ms-8 and connected components but when sync is activated the head unit automatically mutes the rear outputs and fades to the front output. This way the sync voice comes from the rear speakers and when I have a phone call it comes out of the rear speaker but bypasses the processing of the ms-8 avoiding any echo problems. It soumds complicated but it is seamless from a user perspective
2011 Brembo GT.