The XrgModelActor represents an .xrg (previously .sxrweb) model that is to be streamed. In the parameters you can set the material for the model. There are two prebuild materials that can be used in /Plugins/XrgPlayer/Content/ - You can also make your own custom materials and assign them.
Most important is the url the to be streamed object. Make sure the url ends in the actual file name plus extension, and is not the webpage that you use to visit the model in the browser IE. https://stream.senseofspace.io/demos/space-shuttle-new/model.sxrweb and not: https://stream.senseofspace.io/demos/space-shuttle-new/
Lastly, there is a parameter for the StreamController. Make sure it is set to a valid stream controller object.