Sub for Focal Micro's

First of all, I did a search and didn't find any recommendations.

I'm in the market for a subwoofer to augment the bottom end of my Focal Utopia Micro Be's. I'm very happy with the sound, but would like to add some impact. Not necessarily home theater bass, but more dynamic bass.

My system consists of the following:
Krell KAV-400ix integrated
Krell DVD Standard
Focal Utopia Micro

I've looked at REL, Velodyne, and Sunfire. There are no dealers near me so I will be buying on faith and would like suggestions as to which subwoofer will better integrate into my system.

What's your budget?
I use an Electra SW 1000 BE with my micro BE. The sub integrates seamlessly and is very easy to adjust through the remote control.
A friend has the Micros with an Audio Physic sub(the smaller model),and loves it.Many claim his sound is superb,so I must asume the combo works great,as he is fanatical about music.

Good luck
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I use a Velo DD12 in a smaller room with my micro Bes and the DD EQ made blending it with the micros much easier. The display on the monitor once EQd shows a response that I would not have achieved with a non eq'd sub. This is 2 channel music only system and I am very satisfied.
I would say my budget is less than $2K, used or new does not matter to me.

My room is rather large, but because of how my system is set up, I would need a smallish woofer. 12" max.

I'll take a look at the Electra 1000, Audio Physic, and Velodyne DD12. Since I'm enjoying my system so much, I'm not in a rush to buy one so I have time to research.

Thanks for the tips, they should get me started.
I have had that setup. If you have the budget to raise your price limit, go with the Utopia Sub . If not, the REL B2 would work amazingly well with the Micros. Good luck with the search.