This paper introduces research issues on multimodal interaction and interfaces for expressive sound control. We introduce Multisensory Integrated Expressive Environments (MIEEs) as a framework for Mixed Reality applications in the performing arts. Paradigmatic contexts for applications of MIEEs are multimedia concerts, interactive dance / music / video installations, interactive museum exhibitions, distributed cooperative environments for theatre and artistic expression. MIEEs are user-centred systems able to interpret the high-level information conveyed by performers through their expressive gestures and to establish an effective multisensory experience taking into account expressive, emotional, affective content. The lecture discusses some main issues for MIEEs and presents the EyesWeb (www.eyesweb.org) open software platform which has been recently redesigned (version 4) in order to better address MIEE requirements. Short live demonstrations are also presented.