Exemplo de uso do simplexml_load_string

$objXml = simplexml_load_string($xml);

$perfis = $objXml->xpath("/methodResponse/params/param/value/struct/member[name='roles']/value/array/data/value[starts-with(string, 'MU_') || starts-with(string, 'Estado ')]/string");

foreach($perfis as $perfil)
{
$nms_perfis[] = strip_tags($perfil[0]->asXML());
}