I don’t guarantee that the answer you’re looking for is there, but have you checked out kongondo’s guide to Wayfinder? See http://modxcms.com/forums/index.php/topic,34176.0.html for a link to the pdf file. In particular, have a look at the chapter on advanced menus.
Called "The (almost) Complete Guide to Creating Menus in MODx Using Wayfinder", it gives details of all the templates (Chunks) that Wayfinder uses and how to assign CSS ids and classes. I thoroughly recommend it.