Three-dimensional (3D) visual scenes with pluralities of graphic objects require considerable network bandwidth to be transmitted and computing power to be rendered on a user's terminal. This paper proposes an application and transport cross-layer solution for efficiently streaming 3D scenes toward high-quality display. In so doing, 3D objects are scalably coded and are transmitted over multiple streams in a partially sequenced and partially reliable fashion. A rate-distortion optimization framework is developed to determine the optimal level of reliability for every chunk of data in each stream. Compared to heuristical methods, simulation results show that the proposed framework maximizes the display quality of the scene while minimizing the amount of data that needs to be processed by the client's rendering engine.