OK, the demo works for Max & Maya, even in Lightwave and Cinema4D, but you can install it only on one application, so you need to choose between Max & Maya. If you already installed it for Max and you want to install it for  Maya, you need another serial to be able to use Xstream in Maya. And you need to ask e-on the new serial, no need to download the demo again, but you do need a new serial from e-on, and then reinstall Xstream for Maya.