difference of having a 4 channel amp?

THANKS!! just the info i was looking for :) just one more quick question.. so I am presuming I will run new speaker wire from the amp to the 4 speakers in the doors? So should i go along the door trim and go through the rubber grommet to get to the inside of the door panel, or is there some other way to get into the door? Also what do I do with the harness in the back of the headunit? Would I just disconnect it or what, since its not going to be controlling the speakers anymore.. ooo and the remote lead.. do I need a separate one for the new amp, or can I splice the sub amp one and run it to the 4 channel amp? and I am presuming I need a distribution block right? I am running 2 gauge to the trunk, so I should distribute that into 2 gauge for the sub amp and like 8 gauge for the 4 channel, correct? so the tl;dr version: 1. use door trim and existing door grommet to get wire to speaker? 2. leave or unplug wiring harness to head unit? 3. splice remote lead to run to new 4 channel amp? 4. use a distribution block to power new amp with preexisting 2 gauge? I'll shut up after this I promise, thanks :)