Best Sub to mate with magnepan 3.5

Best way to connect a sub with the 3.5,since the x/over point is 250. Which sub now on the market will be the simplest to use & provide the most bottom end for the best price.
I would check into Audio Concepts "Titan"! Check their Web-site too:
hi.. i am a soliloquy dealer .. you owe it to yourself to check out there speakers check out a dealer near you or contact me,,, the S-10 is not only sonically breathtaking but the most beautiful looking unit around ... you will fall in love !!!
Sorry to be contrarian, but I think that the answer to your question is "no sub at all". What you give up in speed and consistency just isn't worth it. My advice would be to spend the same money on electronics that are better controlled at low frequencies--not a perfect solution, since you're playing to the Maggies' weakness, but preferable to a sub.
I agree 100% with Dar. I have owned Maggies and you will spend the rest of your life trying to match a sub with them. The best I have ever heard Maggies sound is in a bi-amped system using tubes to drive the mids and top end and a Crown Macro to drive the bottom end and a Bryston 10B crossover. Crown Macro's can be had for about $1600, the 10B for about $700. Used with high quality interconnects and speaker cable the system can be very special.
get a pair of vmps' original subs w/a decent used solid-state amp & a marchand xm-9 deluxe x-over (24db/octave), if ya have to x-over as high as 250hz. if you can go down to 125hz or so, get a pair of vmps' larger subs... also, marchand makes 48db/octave x-over you may waant to ask 'em about it...