Aren't the 'home' line outs 1V while the 'car' line outs are 4V?
Hmmm, maybe that is changed depending on detected powersource...?

It's not changed. They stay the same voltage. The point being made is that the home plugs and the car plugs are the same outputs. You can't get magical six-channel output by attaching something to the home plugs while docked.