How can I do more complicated queries with an ElementCriteriaModel?
Once you've got your ECM, pass it off to the buildElementsQuery method...

$query = craft()-&gt;elements-&gt;buildElementsQuery($criteria);


This will convert your ECM into a DbCommand object. From there, you can make further modifications to the query... like adding a join for your 3rd party table.

$query-&gt;join('myplugintable myplugintable', 'myplugintable.id = elements.id');
$query-&gt;order('myplugintable.mysortcolumn');

return $query-&gt;queryAll();