Crossover change

The Marchand x-over is only for use with a sub. It will drive your main speakers from 100hz up through its high pass section via your amp. The x-over's low pass section will drive an active sub or an amp/passive sub.

What main speakers do you have? And what subwoofers are you planning on using? Otherwise buying the Marchand is a waste of money!

Do you actually know how to connect an active crossover? Your preamp's main output goes to the x-over's inputs (left and right). Then the x-over's high pass outputs go to your amp's L/R inputs. The x-over's low pass outputs go to the L/R inputs on the two active subs - or the 2-channel amp/passive subs. 

Without a subwoofer or two an active crossover like the Marchand is USELESS! I owned and used an active x-over years ago! The biggest improvement was an increase in headroom/dynamic range - much less amplifier clipping!

The Corn's will sound more seamless/balanced and you will become younger and hipper in spirit (replacing your Nu Balance's with Converse Chuck Taylor low tops).

DeKay

Adding a sub or two (active or passive) through the Marchand x-over will improve the overall bass response and lower the distortion levels in the bass and mids of the Cornwall's.

@jasonbourne52  Thanks for the reply and attempt to help even with my incomplete information.  I have a pair of subs and an amp already.  My subs are DIY Eminence 10" and a yamaha 350W amplifier.  I have used it with great success but just wondered what would happen.  I have read that at about 100Hz is when we hear "stereo" bass.  The crossover change cost me $29 so it is worth a try just curious if others had tried such a thing.  Some of the cross overs have dialed frequencies, mine is fixed.  Thanks.

@dekay  I like my NB.  However, I did quite wearing the white ones years ago.