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
Miller and Kreisel larger 12" sub i have mated with my Maggie mmgis..The system is awesome...Deep top quality bass..it turns the Maggies into monsters,,,Driven by ACURUS 150 amp and pre R11.....and a refurbed ARes-1 table with a VINCENT 08 phono pre amp...as awesome as this economical system can be

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.