By the same logic, the circuit you'll be giving him is a crap shoot. I'll assume you're going to trace the manufacturer's FR into PCD and design a passive circuit. Instead, do the exact same thing but give him eq settings. On the right had side of PCD, just toggle on the active XO feature and you're done. Easier to build, no insertion losses, no cost, etc. And I'm not discouraging accurate response, I'm saying it'll be just as good, maybe even better than any passive circuit. With the sealed alignment, he can shelf the bass the same way. And if you wanna get fancy, there's some free eq software available that's got user configurable eq for more accuracy.
If the OP prefers a passive solution, that's cool too.