?? I've built MANY crossovers by following that book, I don't understand what you mean that it's not for someone who wants to learn to make them, that's how learned. You mean you just need basic electronics knowledge, not specific to crossovers?
Using passive components like caps, inductors, & resistors, would certainly be the easiest & simpliest way to make crossovers, not to mention it's also the most common. I imagine it would be possible to make active ones, too, but that's just adding a bit more complexity that wouldn't be necessary.