Back in 78-79, installed a Clarion(sp?) stereo with triaxials. 6x9s in back, a center in dash, and cant remember what brand under the front seats. Could vibrate the whole car listening to Nugent, Rush, Van Halen LOL.
Having the center dash speaker was much better then just the ones under the seats.
Never had any in kick panel, but think it would be even better vs way mine was.