In this paper a general-purpose procedure for optimizing a resonant inductive wireless power transfer link adopting a multiple-input-multiple-output (MIMO) configuration is presented. The wireless link is described in a general−purpose way as a multi-port electrical network that can be the result of either analytical calculations, full−wave simulations, or measurements. An eigenvalue problem is then derived to determine the link optimal impedance terminations for efficiency maximization. A step-by-step procedure is proposed to solve the eigenvalue problem using a computer algebra system, it provides the configuration of the link, optimal sources, and loads for maximizing the efficiency. The main advantage of the proposed approach is that it is general: it is valid for any strictly−passive multi−port network and is therefore applicable to any wireless power transfer (WPT) link. To validate the presented theory, an example of application is illustrated for a link using three transmitters and two receivers whose impedance matrix was derived from full-wave simulations.