You may be able to implement a system like this with these tools but I think that it would be much more difficult that the other way. Have you used the Digital File Pro download server behavior before? If so then doing it this other way should not be too complex. You will probably want to start with making sure you have a table in your db that has the file names for the products.
If you had this in place then you would just be modifying the existing order details page and creating the new download page.
I would be happy to help you out in either solution, but I'm not sure how the new one you proposed could be put together.