Дмитрий

location / {
                try_files $uri $uri/ /index.php?$args;
        }

header($_SERVER['SERVER_PROTOCOL'] . ' 200 OK');
header('Content-Type: application/force-download');
header('Content-Description: inline; File Transfer');
header('Content-Transfer-Encoding: binary');
header('Content-Disposition: attachment; filename="' . $output_name . '";', false);
header('Content-Length: ' . filesize($file));

$upload = new SplFileObject($file, 'rb');
while (!$upload->eof()) {
    echo($upload->fgets());
}

// тут возможно сначала надо закрыть, потом сбросить буфер
header('Connection: close'); 
flush();
exit;