Regarding the Buttkicers, and I'm being serious, do you guys think I could use one with my wheel chair? Do they need to be bolted onto something or can it just sit beside a chair etc.?
Bolted. The low frequency sound needs to be conducted from the Buttkicker to you. There can't be an air gap, because that would insulate you from the sound.
On the original question, I'd prefer two EP500s to one EP800, and a Buttkicker or any different sub with an EP500 to two EP500s. The rule is that two different kinds of bass will probably give better results than a single kind of bass. And that's because the more alike two bass sources are, the more likely it is that you'll have bass cancellation (which you want to avoid).
