Know what pal, I'll save you *a lot* of pain here and suggest very strongly that you look at PA-based units - JBL, EV, Eminence, etc. Given the size of venue you need efficiency, low distortion and not-so-low frequencies.
PA subs only really need to go down to ~45Hz to sound good in areas that big. I would suggest you go poking around a few PA forums to get some feedback on what you can use.
Best,
Mark