what type of subwoofer is good for ribbons

I am looking to buy a new set of speakers I am very interested in some magnepan ribbon speakers but they dont have enough bass i also heard that you need a special subwoofer for these in order for them to sound right what would make a good subwoofer for ribbon speakers
Like Racamuti, I also run a pair of TBI subs in stereo. They integrate perfectly with Quad 989s. Highly recommended. Robert
I also will throw the TBI into the ring;I am looking at them for my soundlab m2's as well.
Duke (Audiokinesis) is too honorable to blow his own horn. However, nothing prevents me from doing it for him. His SWARM system is outstanding, if:

1) it's in your price range
2) you have the space to place 4 small-footprint subs
3) you can deal with the cabling for #2

I own his Planetarium Betas, of which the SWARM is an integral part. If, however, I were an owner of Maggies, Quads, or the notoriously bassy-shy M-L 'stat, I'd be all over these.
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try to find a panel subwoofer, such as the enigma or sound lab b2.

if you want to optimize coherence, a panel sub is the way to go.

unfortunately there are very few of them, and they may not extend low enough to satisfy some bass enthusiasts.