Two 210 x 2 amps or One 500 x 2 amp.....

Responding to Unsound, I would think you would want the amplifier after the cross over, that way you each amplifer is responsible for only a range of frequencies instead of them all?

I would think biamping is better because it allows isolation of power supplies, transformers, and all that good stuff. Especially is you are running one amp to each speaker. Just my thoughts...