Yeah this group does seem a bit negative on DefTech, but still I agree with what is being said in terms of subwoofer needs.
I was afraid of the answer, but not suprised by it. In fact I think the same would be said about the mains and center speaker. Currently I have 5.25" mains and 4.5" centers. I think the mains ought to be closer to 6+ at a minimum to get the room filled up.
What I have now will have to work for a while. I'll need a pay grade change to think about the subs needed for this room!!
It's more about how subs work in rooms, you can surround yourself with small speakers at closer distance more successfully than you can with subs, altho smaller speakers will struggle more in larger rooms as well.
Low budgets are often better served by buying speakers in steps, start with two good speakers and add from there...
As to subs, I'd generally direct you to either DIY (you can do a couple large subs running off a good amp fairly economically) or proven sub offerings from the specialists like SVS, Hsu, Power Sound Audio, Rythmik, et al.
