Using the Vandersteen M5-HT with a JL e112 sub

I have both Vandersteen 5s and a 2Wq.  In the case of the M5, it's doing "half" the job, while the sub/electronics are tuned complete the job--they are designed as a system vs. as interchangeable components.  The M5, installed between the pre- and power-amp, will roll off the bass that reaches the power amp, starting at roughly 80 Hz IIRC, and on a fairly gentle slope.  There will be residual signal going to the power amp all the way down the bass spectrum because the power amp does need to "see" the whole signal, even if attenuated with each subsequently lower octave.  The Vandy sub has been designed to supply bass along a specifically defined inverse curve, compensating for what the M5 attenuates--this is why the JL may not really integrate.  The Vandy's are also designed to take their cue from the speaker terminals of the power amp.  The sub doesn't draw any power from the amp per se--rather it's just sensing the output as the control signal of what's going to the main speakers, and then integrating to that signal.  Now, if the JL can run off speaker level input AND you can tune the rolloff point and slope to match the Vandersteen sub, then I think you'd have a working solution.

Thanks kj,
I finally found an old post on Audiogon asking the same question, reply matched yours.
I think the sticking point is not so much the rolloff point, most subs allow that, but matching the slope which Vandersteen subs are specifically designed. Though possible, I think it would be more work than it is worth.

Looking through old posts, I see there is an inexpensive crossover by HSU.  Perhaps I should make a new post asking how well it performs.