I am so sorry about the fact that you got a plastic cased X3. However, this image posted by ClieOS
http://i90.photobucket.com/albums/k240/ofey_s/FiiO/X3m-03.jpg
shows quite clearly that the bottom part (which holds the huge battery) is metal. It sparkles in the unfinished edge just like metal and is very thin. like an aluminium shell would be.
Plus the factthat my X3 does not bend and creak like I read in some early reviews. Maybe they changed the case materials after buyer feedback.
Sorry I should be more specific. I was talking about the front part of the casing. The side and back is solid aluminium, but the front sides and front part is plastic with aluminium sheet at the buttons area.