The problem (well, it's not a problem, since they are good lights) with the Alien Bee's is that they used a different mounting bracket for softboxes. The SP's also use a different type of bracket but if I remember right, it is compatible with several other brands, I just don't remember which ones. I still have my SP6400, SP3200 and SP1600 lights but I've always bought softboxes that were sold under the SP label so they always fit on it. I know there are different adapter speed rings you can get for it. You might try doing a Google search on SP Lighting Systems speed ring and see what you come up with.
Mike
