This study presents a multi-criteria optimization approach for the design of a two-stage helical gearbox featuring a split first stage, aimed at achieving a trade-off between transmission efficiency and overall gearbox length. The optimization process employs the Non-dominated Sorting Genetic Algorithm II (NSGA-II) to explore a wide range of design alternatives in the Pareto-optimal space. To facilitate decision-making, the Entropy-based Weighted Aggregated Sum Product Assessment (WASPAS) method is integrated to identify the most balanced solutions based on objective performance. Design variables include the gear ratio distribution, face width coefficients, and shaft parameters, while the optimization objectives target the minimization of gearbox length and the maximization of mechanical efficiency. The results demonstrate that the hybrid NSGA-II and Entropy-Aided WASPAS method effectively identifies compact and efficient gearbox configurations, offering valuable insights for high-performance and space-constrained mechanical systems.