Problems! 2000 Caravan Sport and Infinity Sound

I removed the Infinity CD/Tape/Radio unit from my 2000 Caravan because the
CD player no longer works and I am attempting to replace it with an
aftermarket unit. I bought a dash adapter and wiring kit so I wouldn't have
to cut/splice any of the wires.
Now that I have it installed the rear speakers won't work. Wanting to rule
out bad rear channels in the receiver, I swapped the front and rear speaker
connections. The front speakers still work using the rear channels of the
receiver, so I know the receiver is ok, and it must be something with the
wiring. I tried to get continuity with my V/Ohm meter and couldn't get any
with the rear speakers.
As a last ditch effort, I went to the local Mopar garage and told the guy at
the service counter my story and he told me that "you can put an Infinity
receiver in a non-Infinity vehicle, but you can't put an aftermarket radio
in an Infinity equipped vehicle without replacing the speakers. Each speaker
has it's own amp on the back of it". By that I figured he meant a diode or
transformer of some kind.
Is there any way I can use the stock speakers? Remove the diode/transformer
or something.
What do people usually do in this instance?

Thanks,
Snydley