A weekly seminar consisting of seven composers and one computer scientist was convened for the purpose of exploring questions surrounding how technology can support aspects of the computer music composition process. The composers were introduced to an existing interactive software system for creating new musical interfaces and compositions, which they used throughout the seminar. The group engaged in a user-centered design process to critically evaluate and improve this software. Through documentation of the experience and analysis of composers' responses to a questionnaire following the seminar, we achieved a richer understanding of how technology can support composers' modes of working and goals in the process of computer music interface design and composition. This work also resulted in an improved compositional software system and progress toward several new musical compositions and instruments.