Can this be done with good results????

I got a Magnepan MGMc Center channel for my birthday, it is a special internet only speaker that is a one way ribbon that rolls off at 100HZ, I want to add a cross-over and a woofer that will go to 80hz comfortably, I want it sealed and I will mount it behind the center most likely using hooks and chains to suspend it from the top of my entertainment center (see system pics for details).
I would like this to be as small as possible and a stable 4ohm or better load, this is only meant to compliment the lower vocal frquency that some male voices seem to need to sound best, can this be done with good results using parts express? I have never done anything like this before so how sifficult would it be? please any and all ideas welcome
I do not want to just use my sub for this roll off, I really want to try this thought and hope to get some thoughts from folks that have "been there done that" with building speakers. thanks again all...Chad P.S. 150 watt is plenty good for my taste!