This is where the line output converter could work in theory..
Scion headunit speaker siginals> LOC > Pac TATO > JBL Amp
1) what exactly is in a LOC? does it just convert wires, or are there other electronics going on inside it? what would stop someone from stripping the rcas of the TATO and just soldering those directly to the speaker outputs of the scion
2) on the same token, what exactly is inside the TATO that makes it so special? is it just some resistors and other cheap electronics? could one be made for cheap?
we need an electrical engineer around here to shoot us some diagrams to make our own converter that goes directly from the speaker outputs of the scion unit to the JBL amp!! this person would make a pretty penny on the side from all of us toyota owners that would like to go this route!