passive or active?
what frequency do you want the crossover point to be or should that be adjustable too?
if passive, what impedance load do you want on the woofer and tweeter? 8ohm? 4ohm? 2ohm?
if active what signal voltage input/output do you want? 2V? 4V? 8V?
The crossovers that came with the Alpine SPX-177R were pretty darn flexible, but you still need to match the impedance.