So sorry to not actually answer your question here, because I don't know the answer with SE.... but I am wondering if you've considered moving to the REST API instead of owssvr.dll? It works great for filtering, sorting and ordering.... Also, just as an FYI, you can change the sort in a direct list data connection when you create it. There is a dropdown on the dialog where you pick the columns you want :)
Hilary Stoupa