This contribution is a relativistic theoretical study to characterize systematically the main electronic transitions in a series of hexarhenium chalcogenide [Re6(μ3-Q8)X6](4-) clusters with the aim of understanding: (i) the terminal ligand substitution effect, (ii) the substitution effect of the chalcogenide ion on the [Re6(μ3-Q8)](2+)core, and finally (iii) the significance of the spin-orbit coupling (SOC) effect on the optical selection rules. In all the cases, we found characteristic bands at around 300-550 nm, where the band positions are directly determined by the terminal ligand. However, SCN(-)/NCS(-) presents a different nature of the orbitals involved in the electronic transitions, in comparison with the other studied terminal ligands, located in the near-infrared (NIR) region. All the bands are red-shifted as a consequence of the ligand contribution in the composition of the orbitals involved in the electronic excitations.