Here is my set-up...

2 - 3.5" Cadence ZX351 Series Two-Way Coaxial
2 - 5.25" Cadence ZX551 Series Two-Way Coaxial
2 - 8" Cadence Mallet Subwoofers
1 - 12" Cadence WB12-2sub Wild Beast Sub
2 - Cadence Z5000 Series Amps
1 - Cadence CAP-1R Stiffening Capacitor

I am using a Pioneer Head unit with built-in EQ and 4 chanel 40 watt built-in amp...

I used the head unit to power the 3.5 and 5.25s at 40 watts per... Used one of the Z5000s to power the pair of 8s and the other to poer the 12... The Z5000s are rated at 750 watts each...

My suggestion would be to ditch the 6x9s if you are planning on going with the big subs, no reason to have the three-way coalials... You would be better off to either use 4 two-way coaxials or individual mids and tweets... If you can find a head unit with built-in power you can power the tweets and maybe even the mids with that and save you amps for the bass... You don't need a whole lot of power to push the small speakers 35-50 watts per channel should do... Also the size of your amps will be determined by the size of your subs... You didn't mention exactly how big you are planning on going on the subwoofers, if you plan on going with a pair of 10 or larger and only a single battery I would definately suggest using a capacitor...

If you are planning on trying to hide your head unit, you can mount your head unit wherever you like, and use a remote...

Hope this helps...

Dave Brisco