Hello. I am planning to add amp for front door and under seat woofers. Since I have standard sound system without factory amp I am planning to tap into existing high input wiring behind headunit to route new wires to amp and then back to existing wiring. I am little bit confused because on forums I read that e60 standard front speakers are wired parallel with underseat speakers, but behind headunit there are existing central bass channels.
Am I able to splice from headunit FL/FR+- Central L/R+- to the amp, and back to same wiring?

Added diagram photos, maybe useful for somebody one day.

 

on the e60 headunit M-ASK/CCC there's no output for underseat speakers and no central speaker,in stereo they're connected to the same wiring as front speakers in doors just like you read on the forums,on the headunit there's only output for FL,FR,RL,RR,in HiFi(676) those outputs go to the amp which has outputs for underseat speakers so you're better of buying original HiFi(676 non-logic7) amp like me right now and wiring it to the headunit then to the speakers,buy underseat subwoofers from HiFi or Logic7,rear and front tweeters, then code in VO $676 and other modules to make it work on the original amp because if you don't then the original amp in headunit will fry the amp.
sorry for reviving old post but might as well say it for people who are looking for some info.