You don't need to tap if you buy the factory connectors and make a new harness . If you buy both the male and female you can use that as the "tap." To clear things up I define a tap as cutting the factory wires, or using something like the 3M wire taps that cut into the insulation to touch the wires. Making custom harness is completely reversible by disconnecting the newly created bypass harness and plugging the original connector back into the original unit or connector. I'll include this picture as a sample, it is not audio since I don't have both connectors handy. This one is for the frunk release system and designed to disconnect the car's wiring from the release motor and allows the new controller to "listen" for signal and "inject its own open and close" signal. Now for cars that don't have audio upgrade, a new plug with the line outputs can be created and plugged into the mcu, some cars have the wiring already, and many don't. All S/X MCU have the line out connector on MCU itself, and this amp install document leads me to believe it is always outputting line level audio signal.
Part 3: Amplifier Installation | TeslaTap document for cars with amp wiring
https://teslatap.com/wp-content/uploads/2015/12/primary_amp_650.jpg The green plug is line output for amps. can be use for cars that dont contain the wiring since MCU still has the plug.
For sure do NOT take 12V from just any line to power amps. There are some good places to use at the fuse boxes.
Again, this is probably not for most DYI, but more for a good custom shop to help setup a system that can be disconnected if needed and not impact factory wiring.