I think I found the solution. I updated line 103 in my /download-manager/libs/class.FileSystem.php file to say,
if ( ( get_option(‘__wpdm_open_in_browser’, 0) || wpdm_query_var(‘open’) == 1 ) && ( array_pop( explode(‘.’,$filename ) ) != ‘ies’ ) )
Thank you for all your help!!