04 dodge 3500 rewiring the infinity amp

Has anyone tried to put an aftermarket cd player in 04 Dodge 3500 with infinity system?  After hubby jacked with it for three hours (with original wiring harness we purchased) the radio would power up- just had no sound because there is no amp turn on wire coming from the amp- and nothing obvious to splice into to make it work.  Took it to the radio shop and according to the pros, the entire system must be rewired to get it to work with the exsisting amp, or the alternative is to bypass the infinity amp and replace all speakers.  They tried using a regular wiring harness, failed, and then tried using the DODGE 12 VOLT AMPLIFIER AMP TURN-ON INTERFACE CHTO-01 with no success either.  That's when he told me to bring it back for entire rewire- which also tells me that he has not done it on this particular truck either because he would have known from the start that he would have to do just that- right?  Ultimatly, we would like to keep the factory speakers and add an additional amp and subs...  anyone had the same trouble???  How hard is it to rewire?  Hubby is a phone tech, so he's pretty smart with wiring- just want to one-up him before we get started!!!  Thanks for reading...  Ashley

Metra makes an amp bypass plug for this vehicle.    70-6510