My question is: How, where, or what do I edit to alter the node depth of visible items in the mega-menu?

I've got some menu items that are under several sub-menus (3, 4, & 5 levels down) that I would like to show in the mega-menu, but I'm unsure of what I need to do to make them show up. I feel like it may be in the XSLT somewhere, but I'm no XSL guru. Is it possible? Any pointers on increasing/decreasing the visible node-depth of the mega-menu