In this paper, we study the dynamic behavior of a submerged cylindrical point absorber device simulated in frequency domain. In order to increase the power performance of the Wave Energy Converter (WEC), the system uses three tethers which are connected to Power Take Off (PTO) units installed inside the submerged hull. Considering a generic point absorber with a single tether it is possible to extract power efficiently only from the heave motion because surge and pitch motions barely couple to the PTO. The proposed system is studied in three degrees of freedom and uses one central and two lateral moorings which are anchored in the same point on the seabed. Moreover, it is possible to use a virtual seabed in order to change the length of the moorings. Every PTO unit force has three main components: PTO Stiffness force, PTO damping force and initial pre-tension force which maintains the position of the hull under the sea surface. The main control approach is to tune the PTO coefficients taking into account a specific sea state to increase the power production. After the linearization of the mooring system dynamics using Taylor series, the PTO stiffness and PTO damping matrices are calculated. An analysis in function of the mooring length and the incoming wave frequency was carried out. The mathematical model is based on the potential flow theory and uses the Cummins equation to simulate the performance of the point absorber in the frequency domain. All the necessary hydrodynamic properties were taken by the commercial software Ansys AQWA. Using a MATLAB optimization process, the parameters which maximize the extracted power were found in each case. Furthermore, a comparison among the presented device and a single tether point absorber is presented. The proposed WEC can achieve up to 50% more power production than generic point absorbers.