OK, well, here's the deal: tweeters almost never need 200 watts, or whatever. So you're really gaining almost nothing with passive biamping. Ooh, 2 more watts, or whatever at millisecond peaks.

Active biamping, where the crossover is external, ie, before the amps, lets you use appropriate amps to the drivers. The link to the active/passive article in the article I linked talks about this.

I am the Doctor, and THIS... is my SPOON!