linelevel pre that facilitates balanced bi-amping?

You could also use an active crossover like Bryston's. They allow you to set the high and low pass cutoff frequencies. You set the high pass cutoff below the passive internal crossover and the low pass cutoff above the passive internal crossover. This will still provide many of the benifits of a true active crossover setup without having to ruin the market value of the speakers.

Greg