is one head unit enough to run all that (2 4" splits and rear 6x9"'s) without an amp?
Most head units these days have around 4x45w (peak) output which is fine, but if u find urself turning up the bass/volume a lot the speakers (especially 4") will distort without proper crossovers.
smashed_wombat, yep if u remove the blanks a set of 4" will fit right in.