Hi,
As I mentioned in the Behringer A500 thread I've been experimenting with Bi-Amping my speakers. My speakers do not allow easy access to the crossover so this was with passive bi-amping using my Roksan Kandy and Behringer A500 and using the gain controls on the A500 to balance things out. My conclusion is that passive bi-amping offered no appreciable difference and I have returned the configuration to being driven by the Kandy only. It sounds as good and perhaps a bit better than the bi-amped setup.
If I feel I need more headroom, then a pair of mono-blocks or a bigger amp would be the way to go. Given that the Kandy is 120 watt/Ch into 8 Ohms and I'm in a medium sized room with fairly efficient speakers, I'm figuring that for the time being I'll just stick with what I've got. Should I decide to swap my Theil's back in, I might go shopping for more ooomph.
I suspect that active bi-amping, where the crossover is before the amps and the speaker crossovers are completely out of the picture is really the only worthwhile way to do this.