The direct radiating makes it possible to use passive. You don't have the time alignment issues to deal with. Fully hornloaded LF creates the time alignment issues and makes the passive options much more limited, and very expensive.
@Deang can build you a set.of passives but I think he will tell you that would he in the thousands.
It isn't that complex, we can get you the settings. If I can do it, anyone can (seriously).
I am a Klipschorns fan so my opinion is a little bias,if I had the chance to get a deal on a pair 60th anniversary,my reason would be they rarely cone on market used and if you decide to sell them you can.I am sure the jubilee's are a great speaker and provides life like sound ,I want my speakers to sound good and look good too and to me the 60th anniversary Klipschorns do both.
Do you have 2 good corners? Just one, and thus the reason for enclosed backs? EDIT: I see from previous post you do, then you are golden.
What sub(s) are you running now? That can be an issue, a good fit for subs with Jubes.
If your main criteria is what will sound the best, as you say, there is but one choice.
I'd your question is whether it is worth the extra 20 percent to go for Jubes, in my opinion they are worth more than the typical 3 or 4x what a pair of good used Khorns would run. Couple that with being able add an 1802 later on you can use it for anything. HT, 2 channel, whatever.
What is it going to primarily be used form. HT, 2 ch?
You won't need to worry about diminishing returns until you get to the point of upgrading drivers, center and sub options.
If you have other criteria maybe looks/WAF, space concerns (which doesn't appear to be a problem) or something else I can't help you with that, it is just too subjective.
I have VRDs for 402s and McIntosh solid state on LF with active crossover.
I think you are operating under the mistaken assumption that a separate active crossover somehow changes the sound of your amp, adds coloration, etc. A good active crossover won't do that.