What is best sub to match with Magnepan?

I have the Magnepan 1.7 speakers. I am looking to buy a sub in the near future to pair up with them. Since the planars are fast, I need a sub that is VERY quick. I have a Sunfire sub, but it is not doing the job. Can anyone recommend any brands/models that will work well with the Maggies?
BTW, I'm on a budget too. Trying to get the best bang for the buck.

Current set-up:
Denon AVR-4802 (will be upgrading, not sure what yet)
Olive 03HD music server
Emotiva XPA-2 (500w @ 4ohm)
Sony Blu-Ray player (will be upgrading to OPPO BDP-105)
Magnepan 1.7 Planar speakers
Sunfire TS-EQ10 subwoofer
I would look at a VMPS sub, back when I was looking into Maggies many told me to try this sub, as it has some clay ribbon that you can remove or add as needed to speed the woofer. Another way of thinking about it, is it comes from a company that uses a lot of ribbon speakers, in their own speakers. I have had mine for many years and love it still.
LS, you seem to have a case of the planar bass blues. This is caused by your having discriminating tastes, being able to appreciate what planars can do for you from mid-bass to treble. The fact that you find your sub to be too slow is just further evidence of that.

Sorry, but I have never heard a sub which was fast enough for Magnepans. I have rarely even heard a cone speaker which can differentiate notes in the bottom octave, for that matter - mostly they just thump and thud in a sluggish monotone - unless you spend real money.

The only solution which satisfies me, is to buy a planar speaker with as much low frequency extension as the budget allows. Even ancient MGIII's extend the bass down to nearly 30 Hz, which is really plenty low. To test this, put a 12 dB filter with a 30 Hz crossover in front of your sub, and dial the sub down to 30 Hz as well. Then play a record with lots of bass. I think you will be surprised at how little signal comes through. Unless you goose the bass with tons of gain, of course.

I think you have no choice but to save up for pricier planars. Put it down to the cost of having good ears. Good luck!
I recently took one of my Velodyne HT subs to a friends home for audition, also to show him what he's missing with his Maggie 12's. I thought the F1200 sub integrated very nice. They are very cheap on the used market,or if you want to spend a little more and get a newer version look into the Velodyne HGS series.
Unfortunately, so many folks try to use the LFE connection and sub x-over and place the sub behind the plane of the main speakers. First, I would only use speaker connections so everyone is getting the same feed. Next, open the x-over all the way and adjust the phase and gain to match the mains. And last, place the sub on a plane in front of the mains, maybe a foot or so. If you think Vandys or most any phase-correct speaker, this is the design.
I use a pair of velodyne optimum 8 subs with my Maggie 3.7's. They are a lightning fast responding sealed enclosure sub that blend in perfectly with my setup.

My setup is in a very small dedicated room 14x16x8. Associated gear... oppo bdp-95, cary slp-05, sanders sound esl 300.

I have tried ported subs and they do not blend well with the fast transient speed of the maggies, a pair of smaller sealed subs work much better. Larger subs do not respond quickly enough to blend well.... the 8 inch pair I have put out incredible deep bass that you feel when the volume is cranked up. They deepened the soundstage and make my 3.7's sound like 20.7's.