Subwoofer in my system…

Green Mountain Audio with a sub? I'm thinking I'll need something fast, but maybe not.. I've read a lot of previous suggestions in various forums, but I still don't know what would possibly match up well with the GMA first-order crossover etc. sound. Looking for some suggestions here since there's really no where around me to go audition a lot of different subwoofers.

I have a 2-channel combo with Blue Circle Audio's CS integrated(w/pre-amp output) and GMA Callistos. This combo works well in my medium sized room, but I just want something to fill in that bottom end a bit more. I mostly listen to CDs & watch music DVDs. Looking to spend around $500-$700 new or used, but could possible go as high as 1K.

I'd like to get some feedback here first. thanks!
I had a pair of Europas at one time, and they really needed a subwoofer in my room. I paired them with a Rel Storm, which was ok, but it took a lot more doing to integrate the system than it has taken me with the Rel on other speakers (eg Totems). So, based on my results I'm not sure Rel is a good match (even though I think The Storm III is a fantastic sub and would recommend it with any other speaker).

It would seem to me that the optimal choice would be GMA's subwoofer (the Hammer?), but that's probably beyond your budget. Sorry I can't be more helpful . . .
yeah.. I've read about the GMA Hammer. It is beyond my budget, plus it's not a powered sub and my amp would not supply enough power.

Thanks for the input about the Rel Storm.
I'd give Roy a call at GMA. He was very helpful with my integration of a sub with my Callistos. I'm in no way an audio designer, but I don't believe frequencies below ~45Hz will mess with any of the Callisto's crossover sound. My sub begins at 45Hz and rolls off at about 35Hz and I can't tell where it's located in my room. In addition to the help you get from this thread, I'd consider calling Roy and ask for advice. Feel free to e-mail me if you need further info. Good luck.
If its a first order X-over, you might consider a VAndy 2W or 2WQ.
Looks like I have my answer!

Just heard back from Roy Johnson via e-mail. He suggested the DAYTON 12" Titanic MKIII Subwoofer Kit from Parts Express. He also included a very detailed description of how to hook it up, based on if my preamp outs are active or not. He even had some helpful tips on crossover/polarity settings, and where to place it in the room. How bout that! Not to mention, I gave him a budget of $500 - 1K and he recommends something that cost even less.. Sweet!!

Awesome customer service.