Interactive music systems are an ideal exploration ground for the testing and incorporation of decision-making algorithms and music informatics techniques into real-time applications. The interactive music system, ‘The Harmonically Ecosystemic Machine; Sonic Space No. 7″, is the compositional result of such a collaboration between music technology researchers focused on harmonic accompaniment-generating finite state transducers and sonic ecosystems as interactive music systems. This installation-based system interprets music that occurs in the physical space of a room, from a harmonic perspective, played by both the system itself and any human performers. The resulting data is used by the system to drive the ongoing, generative, interactive composition. The technical details of the system, including an overview of and motivation for the use of finite state transducers (FSTs), the process of integrating FSTs into real-time interactive music systems, the interaction paradigms established, and the experience design for the composition are presented.