A sub doesn't have to be one sine wave, though. You could pitch it down to B, but, for example, use a saw wave with a sharp low cut to keep it in the sub area, and a high cut to make the fundamental a little quieter. A five-string bass can play down to B0 because the first few overtones are what you hear, not the fundamental.
E: never mind we're talking about kicks, yeah F# is probably best.