VW Arteon Sound System Upgrade: Harness Prep and Test Install

All my parts finally arrived 📦! Next step is to alter the harness a bit, to make the install a breeze. We need to cut the iso connectors off and add 5 feet (1.5 meter) extension cables to allow for the amp to be located under the passenger seat.

VW Arteon Sound System Upgrade: Research and Prep

I have a 2019 Volkswagen Arteon R-Line without the Dynaudio system. I want to upgrade my stereo in a 2 phase approach. First, add an aftermarket amplifier to the stock speakers and head unit. Then, replace the stock speakers with something more premium.
While adding the amplifier, I want to use all plug and play connections to allow me to revert to stock easily.