Some more info is necessary:
What type of vehicle will this be going into? How much of a budget? Is there a decent head unit that will be driving the amps?
The loudest box you can build will usually be a bandpass box. They give up a little on the quality of the sound, but they have a tendancy to boom really good if you are listening to stuff like nelly or good techno bass.
There is really no need for two amps to power your two subs, get a decent mono amp and that should give you more than enough power. Budget equipment I would look into is JBL, Crossfire, Kicker Impulse, Kenwood.
Don't get totally caugh-up with the "I must have 600 watts or else" thinking, find a shop that has those sonys and listen to a variety of amps and find the one that you like the best. I can pretty much promise you that if you got a real amp and gave those speakers 600 watts each, you would let the magic smoke out in no time.
