Dayton Audio RS225-4 8" Reference Woofer 4 Ohm has good lowend and should play up to about 1k. if you have it on axis you might beable to get it to play to 2k.. in aout .35 cubes it should sound good down to 70hz..
I want to go 3 way real soon but I would have to get my hands on a active 2 channel amp. But for right know I was go in to run 2 way active on the ppi 900.4. Heres the tweeters I have Tymphany BC25SC08-04 1" Silk Dome Neodymium Tweeter with Waveguide 4 Ohm. Don't think these will like to be crossed that low though. What's your guys opinions on having the tweeters and mids close together on the a pillars or on top of dash.