Myrlyn has it all right (except for the womanizing part).
Source code for GameStudio is not available. Many of your requests (SQL, XML, streaming data) can be implemented using the SDK. For this we support a variety of C compilers and Delphi; C# / managed code is not on the list. The next release of the SDK will be more powerful allowing the engine to be used more like a traditional API library. Keep in mind that there is no way to change the rendering pipeline thus if you want to stream data you will have to do so in your own code, convert the data to a GS compatible format and display it.