Although I have never changed them, there are some things you can change in the options box for polytosubdiv. Choose Modiy>Convertion and then look for a little box directly to the right of polytosubdiv. In this window, you can change some stuff that might make the sub-div smoother when you convert it.
As well as changing the options when you convert there are also various degrees of smoothing visible to you when you are looking at a subd surface onscreen- try hitting the number 1,2 and 3 keys and you will see the change.
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