Active line level crossover with subwoofer out - HELP


Hi.

Helping my friend with another challenge. 
Looking for a line level crossover. His preamp does not have a subwoofer out.

What he wants to do is have a high pass filter between the preamp and his power amp. This so his Spendor BC1’s are spared anything below 40 or 50hz. And, the crossover needs a low pass filter to spare the subwoofer the high frequencies. 
Thoughts? 
Thanks!
perkri
I've used a Marchand electronic crossover in my desktop system for several years. It really gets the job done nicely. I did some not-so-rigorous comparing of the sound w/ & w/o the crossover. I couldn't distinguish any sonic differences with it in vs out of the circuit.

There are a number of models to choose from. Mine has a variable crossover (very handy). But I've heard the models that use a fixed crossover have that nth degree more purity of sound...? Who knows.

Here's mine: 
https://www.marchandelec.com/xm66-electronic-crossover.html

Prices from 2016 were $800 for my XM66 (new). If you can settle on a fixed frequency, the XM9 is $600. Both show up used occasionally (XM66 rarely; XM9 not quite as rarely). 
Hi all!

Quick note.

Thanks for all your help.

Built the Xover yesterday - w some cheap caps - and it worked perfectly!  
Bought 4 different values of cheap caps so we could hear how the system sounded in situation. Those can sit in place until the "good ones" are ordered/delivered

 Numbers and specs are great, but, it has to he heard in the environment to really know how its working.

Sub has integrated nicely. Bass is much tighter/faster/resolved. Sound stage is much better - wider/deeper.

For what is essentially a "lifestyle" system, its sounding really good! Think I may be putting similar high pass system in my 2nd system. Small speakers that would hopefully benefit from those low frequencies "mucking up" the works.