The AudioEndpointBuilder essentially translates the complex language of Kernel Streaming topology into the user-friendly "Endpoints" seen in the Windows Sound Control Panel. If a driver reports a "complex topology" (e.g., a loopback internal mux), the Endpoint Builder attempts to simplify this into standard Windows endpoints to prevent the user from seeing 15 different ambiguous volume sliders.
When an application (like Spotify or Zoom) wants to play sound, it does not ask for "Driver X." It performs the following sequence: audioendpoint