Ok, I've sussed this out and gotten things working. Believe it or not, Best Buy has the solution. If you go to their install bay, and tell them you have line outs and want to go to speaker outs on a factory amp, they'll quite happily charge you for an InstallEdge.com box that wires into the system.

I went to Trashy Shack and got about 40 sets of quick releases, wired up both sides of the wiring harness, and the black box. Plugged it all together, turned the car on and HEY PRESTO works like a champ. The signal gets boosted just enough to make it uncomfortable in the car. Sound is so-so, but it's obvious that nothing is going to help that besides aftermarket amps and speakers. Since I'm loosing my job (My company is going out of business- anyone need a deep IP geek with several years experience at a tier 1 ISP?) I'm going to wait, and enjoy the slightly boosted, and very tolerable, sound I've currently got. Thanks to all those who responded!

Mark.