The point being made is that the home plugs and the car plugs are the same outputs

Physically, they may be ran from a different circuit, but they are the same source.

So, let's see if I get this right: front and rear car outputs come from the same source (the 2 channel mp3) but are split and (optionally) equalized differently/faded. The home output is the same as the car front output - meaning that it has the same equalization done to it, but delivers a signal with a quarter of the amplitude (1V vs 4V)?

/Michael