This paper presents the magnetic resonator piano, an augmented instrument enhancing the capabilities of the acoustic grand piano. Electromagnetic actuators induce the stringsto vibration, allowing each note to be continuously controlled in amplitude, frequency, and timbre without external loudspeakers. Feedback from a single pickup on thepiano soundboard allows the actuator waveforms to remainlocked in phase with the natural motion of each string. Wealso present an augmented piano keyboard which reportsthe continuous position of every key. Time and spatial resolution are sufficient to capture detailed data about keypress, release, pretouch, aftertouch, and other extended gestures. The system, which is designed with cost and setupconstraints in mind, seeks to give pianists continuous control over the musical sound of their instrument. The instrument has been used in concert performances, with theelectronically-actuated sounds blending with acoustic instruments naturally and without amplification.