Hey OP,
Replacing a factory passive XO with active is not usually that simple. There is often a variety of EQ and phase optimizations that take place in the passive XO which must be accounted for in the active to be an equivalent match.
I think I see a lot of need to be creative and experimental in your question, but you are also getting much more complicated. More cables, more amps, more, more.. :)
My major suggestion is keep things inexpensive, so you can try different combinations without breaking the bank. Consider a miniDSP with measurement microphones, and visit the DIYaudio forum