I don't see how to do this with FEC, but since I used an SQL patch from version 1.10.0 to install the FEC configuration menu I may not have all the current options. Perhaps bislewl or numinix can clarify whether FEC does have a solution for guest checkout with downloadable products?

Regarding the auto SQL installer, revisiting the CSS/JS Loader documentation suggests that the auto installer is supposed to run when logging in to the Zen Cart admin panel after having uploaded the FEC files to the server. If this is the case, you really need to state this step explicitly in the installation instructions. Consider this: The first step is to install CSS/JS Loader, requiring login to the admin panel. Hence, the user will already be logged in before uploading the files and (barring a timeout) won't need to log in again for steps 10-12. There won't be any FEC menu item as required to complete the installation in spite of having followed the instructions to the point, and the confusion begins.