The development of Virtual Reality (VR) systems and multimodal simulations presents possibilities in spatial-music mixing, be it in virtual spaces, for ensembles and orchestral compositions or for surround sound in film and music. Traditionally, user interfaces for mixing music have employed the channel-strip metaphor for controlling volume, panning and other audio effects that are aspects that also have grown into the culture of mixing music spatially. Simulated rooms and two-dimensional panning systems are simply implemented on computer screens to facilitate the placement of sound sources within space. In this chapter, we present design aspects for mixing in VR, investigating already existing virtual music mixing products and creating a framework from which a virtual spatial-music mixing tool can be implemented. Finally, the tool will be tested against a similar computer version to examine whether or not the sensory benefits and palpable spatial proportions of a VE can improve the process of mixing 3D sound.