you don't need a friggin capacitor..
no one really needs one...but they do stabilize voltages going to amplifiers. that is the nature of a capacitor; to block AC
Your Panasonic radio probly puts out probably 40-50w X 4..
peak...prolly 15 rms
As for dynomat.. putting it under the carpet is one of the goofiest things I've heard, since there's already sound deadening material there from the factory
ive seen it done and it does work...may be goofy but results speak for themselves.
i too believe in a a decent front stage and have disconnected my rears