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
How about the Magnepan DWM bass panel? With a frequency response up to
7Khz it's certainly fast enough. True, it is more of a deep woofer (40 Hz) than a
sub, but that 40-60Hz boost will provide that little bit of missing foundation for
the 1.7s.

I just got a pair of 1.7s a couple of weeks ago too. I'm not using a DWM, but I
already had a pair of Mirage MM8s, which are *very* quick and lively. They are
9" cubes housing an 8" active driver & 2 passive radiators, powered
by a 1200 w peak class D amp. The diaphragms are very lightweight aluminum
and the surrounds are very compliant and allow for a good excursion. They also
have continuously adjustable volume, 0-360 deg. phase, and crossover from 50-
200 Hz (or none).

Audiovox/Klipsch shut down the Mirage division, but this same sub is still
available as the speakers.com/products/subwoofers/?sku=ESW-M8>Energy ESW-M8. I
have a pair of them positioned in close proximity to the panels, have the
crossover set to the lowest point (50 Hz) and added just enough volume to
flatten the bass down to about 36 Hz, but not so much to be boomy, thickening,
or otherwise intrusive.

I have a friend who's happy with an SVS SB12-NSD with his Maggies. SVS has a
45-day return period, and they pay shipping both ways. That's an attractive no-
risk way to see if you can get one to work for you -- go to www.svsound.com.
I just bought a pair of Gallo TR-3s from an Agoner. I'll let you know how they are with my 1.7s when they arrive this weekend. They're supposed to be spectacular!
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!