What ever happened to just boosting power to the speakers? What prevents you from doing a booster in the speaker wire?
In theory, you can... But the person "boosting" the signal for amplification needs to have a full understanding of all-pass filters, time delay, phase, etc to pull this off. To keep it simple, count the number of channels/speakers you want to amplify and buy that amplifier. Do NOT sum signals, no DSP, etc unless you have a clear understanding of what you can and cannot touch on the factory signal with that DSP.
Last part, you will need to ForSCAN the truck to send the chimes to the gauge cluster since you will now amplify those with no way to turn them down.