Have you called axiom and talked to Brent or JC? They would be able to give you their opinion as well, and have much more experience with different rooms/speaker configurations than most of us....

Personally, i would go with the 800 up front for the lows, then get 2 500's later.... provided you have have enough disposable income/good will with the wife (if you have one) to support another 2 500's down the road.