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
Thanks guys for all the info. I've been playing around with the Sunfire sub I have. Changing positions, fine tuning and level adjustments. It's getting better, now that the Maggies are about broken in.(after 6 months)
Also looking at getting some MYE stands, which will stiffen the panels and I understand helps increase the bass response. I'm just trying to get the best blending of sound I can between the sub and the Maggie 1.7s.
Still tweaking......
Oak244, VMPS went out of business a year ago when the owner of the company died. There are no more new products from that company anymore.
Just got a pair of Gallo Tr3s....they are beyond superb. Like they were made for Maggies! I couldn't be happier.