//a bunch of xml in a string
$xml = $acs_response->AttributeData;

//a bunch of xsl in a string
$xsl = base64_decode($axsl_response->XSLFile[0]->FileContent);

//XSLT Processor wants DOMDocuments

$xml_doc = new DOMDocument();
$xml_doc->loadXML($xml);
var_dump_nicely($xml_doc);  //AN EMPTY OBJECT

$xsl_doc = new DOMDocument();
$xsl_doc->loadXML($xsl);
var_dump_nicely($xsl_doc);  //AN EMPTY OBJECT