We present in this paper a moment-matching method to compute a parametric approximation of the inputoutput (force-to-motion) response of a multiple Degree of Freedom (DoF) Wave Energy Converter (WEC), based on the algorithm presented in [1]. This method allows the user to select a set of interpolation frequencies where the approximating model exactly matches the steady-state response of the target WEC under analysis, while being able to retain key underlying physical properties of the device. Furthermore, we show how to systematically accommodate nonlinear effects using this approximation method, depicting an efficient and versatile approach to compute a parametric representation for WEC design, control and estimation procedures. We illustrate the capabilities and characteristics of this method by means of a study case, using a CorPower-like (heaving point absorber) device. Our numerical analysis shows that, when compared to the currently most-used methodology to parameterise the dynamics of a multi-DoF WEC, the proposed approach can compute mathematical models with the same degree of accuracy and up to ≈ 50 % of improvement in terms of computational time.