Wiring for multiple amplifiers

[rstraub2]

I've searched through this forum for tips on wiring multiple amplifiers while maintaining the factory head-unit. It seams all the tips for doing so indicate to pull the front high-level signals from the front kick panel area, and all the rear high-level signals from the B-Pillars. Is there a reason why folks aren't just tapping the high-level signals right off the harness where it plugs into the back of the head-unit?