We present an instantaneous normal mode analysis of the fifth-order polarizability-weighted densities of states for CS2 for experimentally relevant polarization conditions. We illustrate that polarization selectivity can be used to enhance selectively different contributions to the fifth-order spectrum. We show that the fifth-order spectrum arises predominantly from collision-induced scattering and from cross terms between collision-induced effects and librations, with only a vanishingly small pure librational contribution. We also demonstrate that there is no direct relationship between the third- and fifth-order Raman-weighted densities of states.