Your budget is far better than mine. I would love to be able to purchase that DEQX as I really dont hear too many good things about Behringer.
I believe they are still the designing stages with that center but should be pretty awesome when its done. I will probably just try and pick up a third cbt36 if I am able too, but if not will continue searching for one that can be heard.
For subs I have not decided yet, but will probably stick to what Grant has told me here. He is much more knowledgable than me and I have no problem admitting that.
Are you going to be putting them together yourself? Christmas is a long time away, or is this an overdue present. He really married into the right family.