aerostar with rear seat radio controls

I really have no idea what year model this vehice is, but my installers are telling me that they can not install an aftermarket radio without running new wires to every speaker in the vehicle.  I am having trouble buying this.  It appears that there is a common ground speaker setup at the rear seat controls. 

Has anybody installed a modern day radio in one of these babies?  What had to be done? 

Thanks to all that respond.

We use to do a few of these back in the day.  We did it as follows...run wire to each of the rear 6x8 speakers.  Front dash speakers are common ground, so run new wire to right dash speaker only and then you can use the factory wires for the left front dash.  In order tp find the rear speakers in the back hatch door, you have to basically loosen the entire left interior panel.  The thing is that the speakers in the rear hatch are only 4 inchers, so is it worth it on those (of course it is worth it if you're charging for it).  And finally, the rear factory control will obviously no longer function.