I like your test box. It looks like a handy way to swap values. I might suggest using a large breadboard with various size inductors, capacitors and resistors with bannana plugs on each one. With a whole bunch of patch cords, you can build up any crossover configuration you want.

Some would say "go active" and there is merit in that. But if you want to include a passive crossover, you have to design it with the characteristics of the drivers in mind. The reactance, resistance and non-linear properties of the driver interact with the crossover components, so the driver is an integral part of the crossover filter function. This can be simulated with Spice, or you can do it this way, with a physical model and measure the response.