questo dovrebbe andare, scusa ma ho fatto un errore io ;-)

function getFileContent($xslt = null)
{
$filename = $xslt;
ob_start();
readfile($filename);
$result = ob_get_contents();
ob_end_clean();
return $result;
}

$oggettoDom = domxml_open_file("database.xml");
$nodo = xpath_eval(xpath_new_context($oggettoDom),"//INFO[@id = 2]");
$nodoStringa = $oggettoDom->dump_node($nodo->nodeset[0]);
$xslt = getFileContent('database.xsl');
$arguments = array('/_xml' => $nodoStringa, '/_xslt'=>$xslt);
$trans = xslt_create();
$return = xslt_process($trans, 'arg:/_xml','arg:/_xslt', null, $arguments);
xslt_free($trans);

echo $return;

df -k