Through the design process of a cooperative audiovisual musical instrument, the Evangistrum, we explored users' sense of resonance and agency in relation to technology. The instrument's aim was to promote collaboration, have strong audiovisual congruence and to be intuitive to use while allowing for more complex levels of expression. Using Hartmut Rosa's theory on resonance as a philosophical framework, we explored how cooperation and a sense of agency can be encouraged within an audiovisual musical instrument, and how the interplay between audible, visual and tactile aspects of the instrument influenced users' cooperation and sense of agency. The design was built using Unreal Engine, controlled with commercially available midi controllers, and requires two users to operate. We tested consecutive instrument prototypes through three workshops and a concert. Through this process we gained valuable insight into the role of agency within successful creative collaboration, the complex interplay between the auditory and visual modes, the importance of mindset within collaboration and technology's potential for encouraging resonance.