Being one of the earliest electronic instruments the basic principles of the Theremin have often been used to design new musical interfaces. We present the structured design and evaluation of a set of 3D interfaces for a virtual Theremin, the VRemin. The variants differ in the size of the interaction space, the interface complexity, and the applied IO devices. We conducted a formal evaluation based on the well-known AttrakDiff questionnaire for evaluating the hedonic and pragmatic quality of interactive products. The presented work is a first approach towards a participatory design process for musical interfaces that includes user evaluation at early design phases.