digital radios now?

I have three vehicles that I want to put amps and speakers in. 2004 Dodge stratus 2005 Buick Rainer 2009 GMC Sierra I already have a bunch of amps and speaker boxes from older vehicles. The Rainier and Sierra have Onstar. Does this mean that they have digital radio systems in them and the old ways will not work? I was hoping to just hook into the rear speaker wires to drive the amps and find a switched power wire to turn off and on the amps with. I also am having trouble finding real radio wiring diagrams for these vehicles. Thank you.    Shawn

Stratus That's all I got. Sorry! :) Yes. I HIGHLY recommend interface modules for the others... (Especially if you want to keep the OnStar...)It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."

Hey HamFist - that Digi Radio is pathetic - it still uses analog speakers LOL! As if the analog air-interface isn't bad enough! Why don't they take a page from their French cousins and Direct Inject the audio as their GSM mobiles do (albeit carrier and all)? Honestly, even caveman used digital transmission for long distance communications. We are going backwards! (Written and presented as a joke!! However, whilst the last sentence (above) is opinoon, each paragraph contains at least one fact.)

Thanks for the advice! Where do you recommend buying these interface modules?