By introducing the spatial dimension in the musical creation, a plastic parameter has been imagined already since antiquity, playing both on the structuring of spaces, and on the structuring of the effect of presence. Taking up the classifications of the sign theorist Charles Sanders Pierce, the sound as an index has always been - by its physical capacity to reach the eardrums of the spectator - the main vector of the idea of immersion. Music and sound have thus become credible forms of extended reality. The present project thus aims to work on this notion of acoustic and immersive environment as well as on the "space" of play thus created - a form of extended reality through music, or even music augmented by forms of objects and devices [1] through a study of the creative processes for the composition by the PrÉ device of Jean-Luc Hervé, composer associated with the project. The PrÉ device (for electroacoustic presence) is a multichannel diffusion system based on a singular conception of the relation of sound to place. It creates a sound environment where the audience is surrounded by multiple invisible sound sources. The system is designed to have a large number of independent voices to constitute a large polyphony. It consists of a park that can go up to several dozen sound agents, each associating a nano-computer with a miniloudspeaker, running on batteries. The whole park is connected by a network in HOP web language controlled by a main computer, which allows to free itself from any wiring and to easily hide the sound agents in order to make the device invisible.