[ctuna]

If you read the base system Gide which has some misspelling but still
it the best basic document for upgrading the base system.
Also the info regrading the basics such as why you need the thick
cables for Power and things like impedance matching of speakers
and amps is basic knowledge that is widely available on the Internet.

when you say parallel i am not sure what you mean but that.
But normally amps can take two channels and create two sets
of the same Inputs whose outputs can be equed via the amp.

The block that you show a picture of is not a Harness that runs to
a place in the back where you can mount the amp.
And what about the run wires that for from the amp to the speakers
do you know how you are going to to that.

I don't think that recoding reassigns pins but it does drop the level to
5 volts. And if you have a car made past 3/07 you will need and Icom cable
to do it. The rear channels will drop to 5 volts to if they are not run
off and amp.