You would need to create a dbtech_downloads_filegroup record that has the title, desc, etc info.
After that is saved you would need to remember that groupid then create a dbtech_downloads_fileinfo record
The parentid would be the groupid. Some of the fields really need to match correctly for it to work right.
filetype has to be the right type and filesize has to be the exact size on your server of the file, otherwise it will just give a corrupted download.
filename would be the name of the file, then after the record is created you would take the fileid and add it to the front of the name of the physical file with a -
So filename in the database would be my_download.zip, it generates a fileid of 10, you would rename the actual file to be 10-my_download.zip
It's not something I suggest you do and it would be hard to troubleshoot/support downloads created like this. I understand the pain of uploading large files over the web, but as of now that's the only supported way to add files.