another thing, the HU you want have only have only 2 preout only (front and rear) with 1.8V only, you should REALLY consider getting a HU with 3 preout, front and rear for your 4 CH amp and a non fading for your sub amps, and with a higher voltage preout will give you more power and quality for your amps.
why are you not going step by step ??? just get a good HU first and a good amps and sub kit. a alpine type R 12" will cost you 20$ more than the 2 kenwood and will give you 500RMS (the kenwood are 175RMS each so 350RMS ovrerall).
you can power the 2 pair of kenwood 6X8 with the HU amps, if your planning getting a amps for the speaker you should consider getting more powerfull speakers.
think about it, step by step is way better than rushing on a cheap complete kit !!!
