Magnetic field modulation-based coaxial magnetic gears provide contactless transmission and high reliability, making them promising for wind and marine applications. Conventional designs, however, suffer from limited modulation, severe magnetic saturation, and complex structures. MSMRD-AMG (modulation-enhanced single-modulation-ring dual-modulationx) was proposed. Sum-and difference-modulation harmonics were generated with a single modulation ring, and a multi-path topology was employed to reduce local saturation. 3D finite element analysis investigates its modulation mechanism, air-gap flux, torque, and torque ripple. Results show significant improvements: low-speed rotor torque rises from 40 N·m to 51.9 N·m, high-speed rotor from -10.4 N·m to -12.7 N·m, and torque ripple is further reduced from 14.1% to 10.1% and from 30% to 28.4%. with flux-concentrating Halbach magnets. The MSMRD-AMG demonstrates enhanced modulation efficiency, reduced saturation, and improved torque performance, providing a compact, high-efficiency solution for wind and tidal energy systems.