SABnzbd Completed downloads file permissions

When you created the Downloads/Complete folder, what did you enter in the "Permissions for completed downloads" box? You should enter 777 there otherwise the files/directories will only be visible to the "owner" who created the stuff which in this case would be the "admin" user. This is consistent with the additions you made to your initial post. What you can try to do is on the Share's Advanced options activate the "Set ownership and permissions for existing files and folders" and click Apply. This will result in the already existing files and directories being remapped so that all users can access the files. You can also check the second setting because all files downloaded by SABnzbd by default are owned by the user "admin" and most likely you don't want to access the files using this account.

-Stefan