Mott-type substances with strong electronic correlations and cubic NaCl structure (e.g. MnO, FeO, CoO) undergo a pressure-induced metal-dielectric transition at around 100 GPa, which is accompanied by the loss of the localized magnetic moment. The mechanism of the interrelation between the electronic and magnetic properties at such transitions remains uncertain. As pressures above 10 GPa are out of the present technical scope for neutron scattering, we propose to study the magnetic and structural changes under pressure of the isostructural Mott-insulator FeXMn1-XS with 0 < x < 0.29. Solid solutions of Fe ions in the matrix of Mn metal ions induce chemical pressure, lowering the critical pressure pc of the metal-dielelectric transition.