I recently added a Behringer DSP1124P to my setup. The total cost for everything I needed was about $180.00 (I already owned a RS meter and I needed an external sound card for my laptop).
I'll first say that the combination of the Behringer and Room EQ Wizard (REW) is a VERY slick setup. It's super easy to use once you've been through it once or twice. Then when you really start to understand how the human ear hears the lowest octaves and how your particular sub performs in your room, you really start to open up possibilities with the BFD and REW. The single best thing you can do is to become a member at hometheatershack and read. Just don't let yourself become intimidated, it's actually VERY easy. I was thinking this whole thing was just too much, but I made the plunge anyway. I'm really happy I did, because the results are nothing short of amazing! I've wanted a BFD for about 5 years, and I wish I had got one long ago...
One more point I'd like to make: A subwoofer EQ is really a set it and forget it type of device. While I'm certain an SMS-1 is easy to use, I just couldn't justify $600.00 for such a device. The BFD/REW combo is VERY powerful and VERY flexible. I can't say enough good stuff about owning a BFD.
Before you proceed with the thought that your *need* 8 filters (and who knows, maybe you do), take a quick look at this thread
regarding my latest EQ curves with my BFD. I've learned a lot as of late and I plan to do some additional testing with my specific setup over the next few weeks. I am VERY happy with sound of my setup right now, but experimenting with the BFD/REW setup is fun and only takes my time.
If I can help at all with questions, I'll certainly try. Just understand the guys at hometheatershack are really great and VERY helpful to noobs. It's great to see so many advanced users taking the time to help new people that don't understand anything at all about BFD's or REW.