IMO, it's always worth it to use a subwoofer and go 5.1 vs. 5.0. The lower frequencies draw the most power from your amp. Using a smartly set crossover and subwoofer to relieve your mains from having to do the "grunt" work will benefit the rest of the frequency response from your mains. I suppose if you had absolute top-of-the-line powered main speakers with large built-in subwoofers the line may be blurred slightly, but I am a firm believer in using the right tool (or speaker) for the job. In terms of the "specs" on subs you're finding at BB, that's not the best place to shop for quality subwoofers. Manufacturers of decent speakers (like Polk, Klipsch, etc.) don't make very good subwoofers. Check out SVS, Hsu, Epik, and Lava to start. There are lots of others - check out the other threads in this forum for more ideas. If you can provide a budget, we can offer specific options.