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
lsbklyn

The Rythmik f12 is a fast sub, crossed over at 60/70 hz.. I think with some tuning will  work well. It will also open the Maggies up as the amp driving them , I know impedances can vary and one the reason high current amps seem to gain power in the low end. I guess it may depend a little on what type of music you tend to enjoy most. Is there information down in those lower fundamental notes that you want to hear.

One comment from someone who has owned Maggie’s for the last 15 years, before spending another nickel on anything, get MYE stands.  Unquestionable the biggest bang for the buck in system improvement.  Check out the planar asylum for confirmation.  Best bargain I have found to help your system!

1- If you have the room, the bass panels of any of the Magneplanar Tympani loudspeakers. Secure them to the walls or ceiling for bass down to 30Hz. LOTS of current required. Satie on the Planar Speaker Asylum powers his with 2,000 watts/per Tympani.

2- If you don't (or even if you do), the GR Research/Rythmik OB/Dipole Sub. Each sub has a pair of 12" servo-feedback, free-air woofers in an open baffle dipole frame. Sold as a DIY kit only, comes with the real good Rythmik A370 plate amp.

I use a sealed SVS sub with my -.7s.  Blends really well.   Select the sub based on room size  and add one for each channel 
I run dual SVS PC 4000s in extended mode (flat to around 16 Hz in my 25x40 open floor plan living room.

They operate in stereo mode (my processor has that option, not many do.)

I measure over 106 dB @ 17 Hz (REW w/ UMIK-1, 90-degrees) from across the room. And it sounds ’TIGHT.’

They certainly "keep up" with my Maggies.

I also own a rear 15" Earthquake that is crossed over at 20 Hz for extra low-end (with fear) when playing movies.

The Earthquake is fast, but not as fast as the PC-4000s. So they are relegated to a movie-only role.

The people who say "No subwoofers are fast enough for Magnepans," have been playing with sub-$1000.00 off-brand or REL subwoofers.

I dare those nay-sayers to order *real* SVS stereo subwoofers and proclaim they are not fast enough.

Those people clearly do not possess the budget, time, or inclination for true woofers.

And they will clearly *never* understand, hear (or feel) the other dimensions of the bottom octaves they are missing.