import_xml.php

<?php
$url = 'http://feed.com/export/main/database/?data=objects&format=yandex&v=yandex&key=link_feed=xml';
$file = MODX_ASSETS_PATH.'components/name/file/filename.xml';

if (!copy($url, $file)) {
    echo "не удалось скопировать $file...\n";
}

$xml = new XMLReader();
$doc = new DOMDocument;
$i = 1;
$limit = 30;
$offset = 5;
$xml->open( $file );
while( $xml->read() ) {
    if( 'offer' === $xml->name ) {

        if($i > 1){ $xml->next(); }

        if($i === 1 && $offset !== 0){
            for($j = 1; $j <= $offset; $j++){
                $xml->next();
            }
        }

        $node = simplexml_import_dom($doc->importNode($xml->expand(), true));
        $array = json_decode(json_encode((array)$node), true);
        $internal_id = $xml->getAttribute('internal-id');
        echo $internal_id.'<br>';

        $product[$internal_id]['internal_id'] = $internal_id;
        $product[$internal_id] = $array;
        $product[$internal_id]['description'] = (string)$node->{'description'};

        if($i >= $limit){ break; }
    	$i++;
    }
}

print_r($product);