[Strangler Lewis]

I think Eats Shoots and Leaves says this breaks down according to English vs. British. I don't recall which is which, but one side will say Mr. Jones'; the other, Mr. Jones's. I think both agree that plural is simply s', e.g, the dogs' bones. Your example complicates matters because it is a name that ends in a plural. I would go with s' or, more likely, try to evade the problem as LSPE outlines above. To be even more uncontroversial--or less controversial--you might say "the web site designed for/run by/etc. XYZ Productions."