That is a PA driver. I use a $1,200 active 18" Yorkville driver powered on 1600 watts in a horn loaded enclosure when I DJ. You don't need 21 cubes - they're not designed for that. Most PA enclosures are relatively small compared to those in the car audio world. Why? Because they aren't meant to have linear response or have very low end extension. Their xmax is typically rather low too. They are also meant to cover frequencies above subbass - I typically leave the LPF on at 150 or so.
A pair of them absolutely knock your head off in terms of sheer output. They will reach levels of 136+ decibels several feet away in a medium sized venue. The whole venue rattles. My equipment near it dances all over the table. I wear in-ear canal earphones to protect my hearing when I do it for several hours.
However, it really doesn't have any place in a car. Pyle Pro gear is better than their automotive division, but I still wouldn't touch it. Although I imaging a pair of those would get plenty loud even for me at a club.
Might be a fun project, though. Just don't expect to want to hang on to it //content.invisioncic.com/y282845/emoticons/smile.gif.1ebc41e1811405b213edfc4622c41e27.gif