Though the advantages of direct Matrix-based Dual-Active-Bridge (MB-DAB) converters have been highlighted in recent literature, their complete set of modulation possibilities are yet to be analyzed. This holistic study of modulation modes is presented in the paper, which divulges the power transfer boundaries of possible modulation modes in the front-end half-bridge (FE-HB) and front-end full-bridge (FE-FB) MB-DABs, and highlights the acceptable modulation scheme(s). For an optimally designed 1 MVA modular MVAC-LVDC conversion stage of Solid-State-Transformer (SST), the FE-HB MB-DAB configuration proves to be a better alternative compared to FE-FB variant in terms of the power transfer boundaries, apart from the other topology related benefits highlighted in literature. Simulation results for modulation of the full-scale 1 MVA SST's 35.1 kW(pk) submodules validate the mathematical analysis. Further, a scaled-down 1.4 kW(pk) experimental validation verifies the FE-HB MB-DAB converter's working principle.