So... I assume that means only the frequencies allowed to pass from the subs to the mains via the mains amplifier are presented by the mains... and... that the controls on the subs provide the various adjustments of how much and how those frequencies pass to the mains (at least for the JL subs).
I did take a look at the JL Audio CR-1 crossover reviews and found this discussion of how the reviewer connected it and dialed in the crossover - which is also very informative.
https://www.soundstageultra.com/index.php/equipment-menu/537-jl-audio-cr-1-active-subwoofer-crossove...
It appears that discussion, moreless follows your suggestion above.
This all makes sense and is very helpful.
I did take a look at the JL Audio CR-1 crossover reviews and found this discussion of how the reviewer connected it and dialed in the crossover - which is also very informative.
https://www.soundstageultra.com/index.php/equipment-menu/537-jl-audio-cr-1-active-subwoofer-crossove...
It appears that discussion, moreless follows your suggestion above.
This all makes sense and is very helpful.