Throwing an RSS Feed into a getPage call

// Target outputArray
$outputArray = array();

// MODX Resource query
$query = $modx->newQuery('modResource');

// add your $query criteria using methods like $query->where(), then:

$resources = $modx->getCollection('modResource', $query);
// Iterate
foreach ($resources as $res) {
    // key the outputArray elements off the raw publishedon date value
    $outputArray[$res->publishedon] = $res->toArray(); 
    // Fetch TVs if you need them and add them to the array element $outputArray[$res->publishedon]
}

// Now get RSS feed into another array
$rssItems = $feedGettingClassInstance->getFeed('from_somewhere');

foreach ($rssItem as $item) {
    // key the outputArray elements off the pubDate value
    $outputArray[$item->pubDate] = $item->someMethodToMakeArrayWithSameKeysAsResources();
}

sort($outputArray);

$output = '';
foreach($outputArray as $element) {
    // process with chunk named $tpl and add to output
    $output .= $modx->getChunk($tpl, $element);
}
return $output;