How much do those little mono's cost? I'm in the procecss of putting together a system for my vehicle with some focal speakers. Looking for some good cost effective power.
http://www.mitekfactoryoutlet.com/products/brand.cfm?brand=4&detail=ok&PN=XTANT1.1I$350 direct from factory. They are nice little amplifiers. Very small. Very dynamic for a car amplifier. And the best part --- their efficiency doesn't make your car beg for an alternator upgrade. Auto is the ideal application for class d all around.
Also, Danny is right, tweeter and woofer as close as possible. I would try Woofer and tweeter in the kick panel if you have a large kick panel area and don't mind the encroachment on your foot space; woofer in door and tweeter in kick if you want to minimize space.
If all that doesn't work out, get a little crazier with the crossover and eq:
http://www.altomobile.com/html/ucs_pro.html48db crossover slopes available with that one. Combined with 5 peq bands per channel, time delay, and a bunch of other nice options, you should be able to integrate drivers in less than ideal locations pretty easily.
Having said that, I used to have an active setup, but found a good deal on some nice mb quart components with passive crossovers, and have been just as happy.
There's something to be said for a tried and true passive crossover and less processing...