Libration Perturbed is a performance and an improvisation instrument, originally composed and designed for a multi-speaker dome. The performer controls a bank of 64 virtual inter-connected resonating strings, with individual and direct control of tuning and resonance characteristics through a multitouch-enhanced klavier interface (TouchKeys). It is a hybrid acoustic-electronic instrument, as all string vibrations originate from physical vibrations in the klavier and its casing, captured through contact microphones. In addition, there are gestural strings, called ropes, excited by performed musical gestures. All strings and ropes are connected, and inter-resonate together as a ”super-harp”, internally and through the performance space. With strong resonance, strings may go into chaotic motion or emergent quasi-periodic patterns, but custom adaptive leveling mechanisms keep loudness under the musician’s control at all times. The hybrid digital/acoustic approach and the enhanced keyboard provide for an expressive and very physical interaction, and a strong multi-channel immersive experience. The paper describes the aesthetic choices behind the design of the system, as well as the technical implementation, and – primarily – the interaction design, as it emerges from mapping, sound design, physical modeling and integration of the acoustic, the gestural, and the virtual. The work is evaluated based on the experiences from a series of performances.