zetener

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.