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
A simple solution is to get a set of filters built into RCA plugs and a RCA splitter on the pre-out. They are much used in car audio setups and work well. Search on eBay for rca plug crossover.
Thanks! Sent Quad an email to confirm no issues with running two separate and very different amplifiers from the single preamp out. Really hope this is a viable option!!!
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.