this is the xml entry that you have to use, to only let ps2 classic games show up in a specific place. you could modify any categories gamefolder and replace its entry with this. the problem is, if you only want to let it show up there, you have to edit category_game xml, cause it will show ps2classics, too. but this will break album function in game category
credits to aldostools and his xmbm+ edits.
<Query class="type:x-xmb/folder-pixmap" key="install_2p" attr="install_2p" src="xcb://localhost/query?sort=+Game:Common.titleForSort&cond=Ae+Game:Game.category 2P"/>