Yes this is the first step, in addition to determining the crossover slopes used. Then one would need to run a frequency response curve at the input to the individual speaker drivers to determine what, if any, response contouring (voicing) takes place in the passive crossover (an RTA would do this). If there is some maniupulation of the response in order to "voice" the system, this could be duplicated by an external equalizer - or not - this is totally up to the user.

Then, the polarity of the drivers would need to be established for flattest response through the crossover region - this could be determined by looking at the response of the system on an RTA (like TrueRTA). The final step would be looking at the system on an RTA and establishing the volume levels for the induvidual speaker drivers for flattest response.

Of course, one could deviate somewhat in crossover frequency and slope, in addition to "voicing" options with an external equalizer, in addition to adjusting the relative volumes of the speaker drivers. "Flat" response on an RTA does not necessairly yield the best, most realistic sound - this is one beauty of an active setup since the character of the final sound from the speaker is completely in the hands of the consumer.