It seems what you want can be achieved through a INNER JOIN
:
$dataProvider=new CActiveDataProvider('Item', array(
'criteria' => array(
'with' =>'sector',
'condition' =>'t.sector_id=:id',
'params' => array(':id'=>$id),
'order' => 'fi.item_id DESC',
'join' => 'INNER JOIN featureitem fi ON fi.item_id=t.id',
)
));