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
Nearly a decade late but:
What is best sub to match with Magnepan? 
Four.
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Don’t know the best but my local dealer always ran Rel subs with Magnepans and his setups always sounded sublime.  The man had golden ears. 
I used an old M&K with mine when I had them. It was fine.
Using a single REL T5 with .7's. A DSPeaker Anti-Mode 2 is also in the mix.  Works fine.  It took some experimentation to position the REL but that's part of the game we play. I may get a second T5, maybe not.