I hate to be the heavy, but I would not even bother trying to bi-amp in the way you are considering. In short, you won't be getting any better sound from your system.
Believe me, it has been tried many times, and as you can see very few amps allow you do this without going through hoops.
Unless you just have to try it out, I would put my money and efforts into getting the best equipment for the speaker that you love.
Bob