Perhaps the biggest limitation of interactive EC is the fitness evaluation bottleneck, caused by slow user evaluation and leading to small populations and user fatigue. In this study these problems are addressed through the proposal of new user interface techniques for interactive EC, which allow faster evaluation of large numbers of individuals and the combination of interactive with noninteractive evaluation. For the first time in the interactive EC literature a set of rigorous usability experiments compares these techniques with existing interactive EC and non-EC interfaces, for the application domain of sound synthesis. The results show that a new user interface for interactive EC improves performance, and further experiments lead to refinement of its design. The experimental protocol shows, again for the first time, that formal usability experiments are useful in the interactive EC setting. Statistically significant results are obtained on clearly-defined performance metrics, and the protocol is general enough to be of potential interest to all interactive EC researchers.