The U.S. Army Research Laboratory-Human Research and Engineering Directorate, Advanced Simulation Technology Division (ARL-HRED-ATSD) performs research and development in the field of augmented/mixed reality training technology. As part of this continuing research, 3D spatial audio concepts previously developed have been further matured culminating in a desktop demonstration system and a set of novel real-time approximations for sound propagation in a true 3D environment. While much attention has been given to the visual representations in augmented/mixed reality systems, true 3D spatial audio has generally been overlooked. The 3D spatial audio simulation has tremendous utility in immersive environments used for augmented/mixed reality training. This technical challenge has been thoroughly researched for many years and many approaches have been designed, developed and studied over the years but yet still a viable system is lacking which exploits the availability of high fidelity and low-cost gaming engines. The basis of these studies is that while immersed into an augmented/mixed reality training environment, a soldier must be able to sense the direction and distance of sound sources from virtual components as he moves through the augmented world. The developed concept is based on true 3D geometry computations and virtual mixers which preserve the sound source implementations. Representation of the 3D spatial audio field is demonstrated using a discrete transducer desktop system which fully supports all six primary sound field directions; up, down, left, right, front, and back. This paper describes the implementation of real-time approximations to sound propagation in realistic dismounted environments, a novel demonstration system to produce the 3D sound, and presents the remaining challenges to be overcome. Designs for the next phase of experimentation are also discussed along with the remaining challenges required to provide 3D spatial representation in real-time to immersed humans on the move in augmented/mixed reality training systems.