There are two forms of bi-amping: active and passive. Active involves building crossover networks that are applied after the pre-amp and divide the signal into separate signals for the different drivers of the speaker. You are going to be doing passive, which involves retaining the crossovers inside the speaker and instead simply splitting the pre-amp signal with a Y-splitter (see here for a pretty hefty example of such a splitter). The splitter's two outputs then go to the two amp channels that are used to drive the single speaker.