Unfortunately, there is not a way to Import your PowerPoint files into your MediaShout Library in MediaShout 6. I apologize for the inconvenience that this creates, I can see how that would be extremely useful.
For now, your best bet would be to continue doing what you are doing to manually add the songs into the library. Or, you could simply insert/import the PowerPoint into your Script to use for each Sunday. You would just have to do this each time that you'd like to use that PowerPoint file.
Please let me know if you have any other questions.