As for preamp, you may not need one. It's highly unlikely that you'll be disappointed. In the simplest design, a 2-way crossover has a single pair inductor-capacitor: we are dealing with first-order crossovers. While a series network is theoretically equivalent to a parallel network, this only applies when impedance correction circuitry has been added. And consequently, there is no phase distortion due to the time delay of frequencies relative to one another.
nest...