There is no straight forward way about it. Each vendor has its own format for the feeds. So no matter which path you choose you will need a custom script or to customize existing code. EP is good to play with, but that's about it. You need to customize it at the end of the day. Filter out currencies, setup attributes, format product descriptions assign products to categories and so on, based on the feed format.
If the vendor has a structured xml feed, I would set up an some xml mapping script and populate the database. See the XML parsing functions in php.net
http://www.php.net/manual/en/book.xml.php. In some cases the available feed is so bad, that is faster to write a script for a bot and crawl the products from the site directly.