Revisiting the current-driven and field-induced insulator-to-metal transitions in the nodal-line ferrimagnetic semiconductor Mn3Si2Te6

${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$, a quasi-2D ferrimagnetic nodal-line semiconductor with ${T}_{\mathrm{c}}=78$ K, exhibits strongly angular-dependent colossal magnetoresistance (CMR) in its magnetically ordered state, which is featured by the development of a unique metallic state under magnetic fields along the $c$ axis. Recently, a peculiar chiral orbital current (COC) state has been proposed to exist in this compound, evidenced by the effective manipulation of magnetotransport properties via applying electrical currents. A field-induced insulator-to-metal transition (IMT) and field-controlled electron scattering off COC domain boundaries thus serve as two feasible origins of the CMR in ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$. Here, we further explore the current- and field-driven variations of electronic states in ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$ by scrutinizing its electrical transport, thermoelectric, and thermal transport properties. A combination of $I\text{\ensuremath{-}}V$ characteristics and Ettingshausen effect studies allows us to pinpoint the predominant impact of Joule heating on triggering the current-induced IMT. Measurement of the Seebeck effect unambiguously reveals a reduction of the band gap occurring concomitantly with the CMR, in accordance with the field-driven IMT scenario. A remarkable enhancement of thermal conductivity below ${T}_{\mathrm{c}}$ is observed when magnetic field is applied along $c$ but is absent under in-plane magnetic fields. Such an anisotropic positive magnetothermal conductivity most likely reflects increase of the phonon mean free path stemming from the field-induced suppression of boundary scattering, hence it implies the presence of certain types of field-tunable structural domain walls in ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$. Our findings not only underscore the intricate interplay between the spin, charge, and lattice degrees of freedom in ${\mathrm{Mn}}_{3}{\mathrm{Si}}_{2}{\mathrm{Te}}_{6}$, but also point toward cooperative mechanisms for its CMR: Whereas the field-driven IMT appears to be the most essential cause, domain boundary scattering may still play a secondary role.