I wouldn't get the 4B for anything except rear speakers on a home theater. 120 hertz is just too high to start rolling off. As Adam said, the higher you crossover your sub at, the more directional it becomes- which is bad if you only have one subwoofer. Like I said before, if you get a subwoofer for each channel, this is no longer an issue. If you cross over your subwoofer low enough, supposedly you can't tell where the sound is coming from, although I always could. I suspect this has more to do more with the acoustics of my room than any super-human hearing ability I might have. The 5B would probably be fine, although it will be more demanding of your subwoofer than the 6B. With the 6B, there is less of a need to get a sub for each channel, because you will be crossing the sub over so low, like say 50 or 60 hertz, that directionality should not be an issue at all.