you would need more than three amps if you chose to go oldskool, you haven't mensioned a sub, and you will definitely want one. even if you don't use one in the studio (I use big quested monitors usually without a sub) the road noise and engine of the vehicle will do a lot of cancelation and a sub becomes necessary to make the music real again.

I'd personally keep the zapco for simplicity and reliability's sake, and coming from someone who still has a soundcraft mh3 console and crest amps for his studio, that's a hard thing to say. but car audio is much more of a compromise than pro audio/recording is.

I would also suggest a dsp processor such as the alpine h800 or Rockford 360.3 to control and tune all of this wonderful gear. the car is not a treated room and lots of nulls and mostly peaks exist to ruin the musical experience.

all in all, have fun and keep us posted as to what you use, great gear choices so far.

p.s what kind of car is this going in?