Actually, the pre-amps in today's heads are pretty good...for instance the P1R from Pioneer has time alignment, 13 band, crossover, etc built in.

The amps....ahhh I heard better , but they are light years ahead of 5 years ago. A few years ago, Pioneer came out with the Mosfet amps in the heads that were pretty powerful. I'd say that you can get away with an amp in the head so long as it has a cross-over on it, and you plan on adding a sub...then you can get pretty good results, even on the stock honda speakers.

If you are going with entry-level components, I think that head power is fairly acceptable if you are responsible with the tone and volume controls...if you are getting high-end comps, amp them...your ears will be happier.