Tangible user interfaces for manipulating audio and music focus mostly on generating music on the spot, but rarely on how electronic musicians balance preparation and improvisation in staging live performances or on how the audience perceives the performances. We present mixiTUI, a tangible sequencer that allows electronic musicians to import and perform electronic music. mixiTUI is developed in collaboration with electronic musicians, with a focus on live arranging, on visualizations of music, on tokens that represent key elements in live performances, and on how the audience experiences the tangible interface. We present an evaluation of mixiTUI in a concert with 117 participants and argue that mixiTUI improves both the audience's and the musician's experience.