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Nonlinear and internal coupling effects in oscillating devices often require advanced and complex modeling that goes beyond overly-simplistic linear models suitable for early design stage. As ocean testing is comparatively expensive and risky, wave energy developers rely heavily on wave tank experiments to test device dynamics, performance and survivability. Not all physical processes — such as viscous effects or power take-off systems — scale well. Careful design of physical components remains crucial to ensure that results from small-scale tests reliably represent real ocean behavior, making scaled experiments both technically challenging and essential for wave energy development. This study presents the design, validation, and dynamic investigation of a 1:10-scale, direct-driven point absorber wave energy converter moving in six degrees of freedom under regular and irregular sea states. A passive linear eddy-current brake is implemented as the power take-off system to emulate a linear damper. The results reveal that multi-degree of freedom interactions significantly alter system behavior, producing coupled peak responses that differ from the natural period. Sway instabilities driven by parametric resonance highlight the limitations of monochromatic testing. In irregular sea states, their impact on power capture primarily affects lower-energy period sea states that are not excited in the coupled peak response. The capture width ratios reaches its maximum of 26% under intermediate damping in the shortest energy period, while the optimal damping ranges between 123 and 314 N s m−1 for all considered sea states. A reduced 3-degree of freedom numerical model is validated and shown to perform well in the most linear sea states, predicting capture width ratios within 0.84–1.12 of the experimental values despite not accounting for sway instabilities. © 2026