I FOUND THE SOLUTION but it's not a pure php solution, but works very well. A little hack for everybody who lost countless hours, like me, to fix this
$dom = new DomDocument;
// main object
$object = $dom->createElement('div');
// html attribute
$attr = $dom->createAttribute('value');
// ugly html string
$attr->value = " this is a really html string ©
with all the © that XML hates!";
$object->appendChild($attr);
// jquery fix (or javascript as well)
$('div').html($(this).attr('value')); // and it works!
$('div').removeAttr('value'); // to clean-up