Subwoofer hook up

Perhaps a dumb question, but here goes. I'm getting a pair of small Magnepan that will no doubt benefit from a sub. I'm using a NAD C372 integrated that does not have a dedicated sub out jack (it does have pre amp outs). So what I'm wondering is: if I use the high level inputs on the sub (Athena AS 400)...where I run speaker wire from the amp to the sub, then from the sub to the speakers....will the adjustable crossover in the sub filter the signal going to the Maggies? In other words...if I set the xover at 80hz, will that prevent the Maggies from seeing lower frequencies? Thanks for the thoughts.
I just read the manual online and it certainly isn't clear about how the circuit works but it looks like the answer is no,it will pass the fullrange signal. The only real way to know for sure is to hook it up and see for yourself. I personally wouldn't pass the signal through the sub anyway,I prefer a direct connection for my speakers. I use speaker cables with spade ends for my speakers and put speaker cables with banana ends on the same posts on the amp to run to my sub. I then tuned my sub to blend nicely near the bottom of my speakers range and it all sounds great.
As it turns out, it doesn't matter anyway. After setting up the Maggies, there is more than enough wonderful, musical bass. As a previous Maggie owner, I should have known this, but feared that the smaller MG12 would be deficient. It isn't!! sub for 2 channel!