how can you choose a 1 preout deck if you need to plug 2 amps on it, you should try to find one with front/rear and non-fader preout with a good voltage.
why builting a big sound system with lot of cheap stuff, why do you need 4 sub when you can have just 1 or 2 but way better and performant sub.
Why are you not begining by 4 good speaker and get a 4ch for them after than buying 4 crappy speaker that doesnt really need amps to power them.
you should really consider going step by step, than rushing to get the more stuff you can at the cheaper price you can... just my advice
