Unless you are bypassing the internal passive crossovers of the 804 you will not need an active crossover such as the Marchand. Typically there are two sets of binding posts on the back of the speakers that are strapped together for single amp use. One set goes to the internal high pass filter and the other set goes to the internal low pass filter. You biamp by separating the terminals from each other on the back and using two amplfiers that have the same gain or one of the amps will need to have variable output to control the gain.
