I want for the sub to get down to as close to 20hz as possible, as well as being loud. I am mainly leaning towards the ED a2-300 for $415 shipped. I am also looking at the HSU STF-2 Is there any other subs in the price range that is better then that sub?
Both are nice choices... the eD will likely give you better extension, i'd put my money on the HSU and a few others for output capability though.
Personally at that general price range, I'd go for the Epik Legend. Two 12" drivers = just a ton of radiating area! It probably has the best chest slam as well as a more smooth response curve.
re: Horns - they have a lot of volume capability thanks to their efficiency, but they're not going to have deep extension unless they're huge. They're good for parties, but not really home theater.
Well, that's not quite true either. Some horns are great for home theater. BUt chances are you have to assemble them yourself ie a THT, or they're well out of your price range ie Danley / JTR stuff.
The dual sealed is IMO the best choice.
If you're okay with stretching the budget, you can get two Epik Legends for 800 dollars. That's pretty much unbeatable!