I haven't used this module, but have you tried looking at the array the feed is stored as with print_r or similiar? I imagine that it has these XML nodes, but getting to them may be un-intuitive.

Also this turned up in a quick google search: [#ZF-1863] Zend_Feed API is counter-intuitive and does not support many feed types by default - Zend Framework Issue Tracker

More tidbits in the search: zend_feed namespace tags - Google Search