2014 Prius C2 Stereo Upgrade

I have one installer I work with in MA. The upgrade is kind of his idea and kind of mine.

I have in the front: Kenwood Excelon Head unit
Hertz Components in Doors with Acrylic Mounts and Hushmat around them. There is very little space for them to vibrate wildly because of the way they are installed between the door and door panel.
Hertz 4 channel amplifier installed under the passenger seat--because of the amps power the speakers don't push it hard resulting in no distortion.

in the hatch area: Hertz 12" energy sub
Alpine PDX4 is used to power the sub bridged down

It sounds very much improved but my goal is a 3 way system with a processor like an Audioson Bit 10 and a battery upgrade like an OPTIMA or XS. the midranges and the tweets will be in the a pillars which will be redone in fiberglass and the amps will be under the seats. I am interested in whether or not he thinks Tyler's idea is workable here as he is using only 8" subs.8" subs don't go down as deep as a 10 or 12 in frequency response.