The XrgModelActor represents an .xrg 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.
NOTE: In case you don't see any textures, make sure that the Material of the XrgModelActor has a Material assigned. It can be the Unlit (for photogrammetry) or PBR that comes with the plugin or any custom Material.
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.xrg 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, otherwise the stream won't start.