Wearable robotic exoskeletons are frequently explored for their efficacy in rehabilitation and in assistance in daily activities in people with motor disorders, yet relatively few have convincing evidence for use. Here we describe a cable-driven ankle exoskeleton that provides assistance to the ankle in sagittal and frontal planes simultaneously, aimed for persons with dropfoot and excessive inversion after e.g. stroke. In this study, we propose a multi-objective human-in-the-loop optimization that adjusts exoskeleton control parameters to improve two independent gait quality measures, specifically foot segment kinematics and step length symmetry. We illustrate how the identified solutions represent a balance between the two objectives.