NICT has developed a multi-view 3D video display system with a 200-inch screen (REI display). In this system, several viewers can simultaneously view natural 3D objects from their respective viewing positions without special glasses. We proposed a 3D audio system using multiple vertical panning (MVP), which is compatible with REI display systems. However, the practical realization of our proposed system is obstructed by the assumption that the position of its sound sources is continuous. In this paper, to develop a practical system, we evaluated the effect of the discretization of sound source positions on the sense of presence by performing two audio-visual psychological experiments where the horizontal and vertical positions of sound sources were discretized. 3D videos were presented to viewers wearing glasses in both experiments. The results of the first experiment showed that viewers failed to discriminate differences of the sense of presence with ten or more loudspeakers. In the second experiment, viewers failed to discriminate differences of the sense of presence even if the vertical position of the sound sources was discretized with two steps. We conclude that a practical system using our proposed system can be constructed with five horizontal and two vertical steps of sound source positions.