Gaze-tracking technologies can enable computer access for users who are unable to use standard input devices. However, using gaze as input poses challenges for interactions that require visual planning, like playing a digital instrument. We explore how multimodality can support eye-controlled musical expression by designing different multi-modal gaze interactions around a digital instrument we call Dueto. We tackle three design goals: creating an instrument that is explorable, easy to learn, and allows feature controllability. We showcase three different multimodal interactions for music playing such as eye gaze only, gaze + switch, and gaze + partner mode.