personally i wouldnt bother with an 8" sub as it wont be pushing enough air to give you any deep low down bass.

i changed my head unit to a pioneer dvd, did the 220uf 100v non polarised capacitor mod(found on this forum) to my front speakers cutting the bass and allowing for only mid and high, and then put a 1600 watt active 12" vibe black air 2 in the trunk.
sounds awsome with lots of low end bass in the back but clear vocals in the front. sweet!