Do you want to achieve reflections similar to the table in the showcase? Using an environment map is the right approach for this. However, the reflections highly depends on the material configuration. It might be easier to provide useful feedback if you show you the rest of your material is set up.
Apart from the reflections, the demo uses ambient occlusion maps in order to create the realistic lighting in the room. Achieving a similar effect just with some lights and without post-processing is not possible with three.js. If you google “ambient occlusion maps”, “lightmaps” or “baked lighting”, you will find many resources for this topic.
The showcase is now many years old and at that time glTF was not that established like today. The project used a custom JSON format for defining the scene. If you want to develop a similar application now, I would recommend to use glTF.