The influence of the anharmonic vibron-phonon coupling, arising on account of a `dressing' effect, on the characteristics of the lattice subsystem in quasi-one-dimensional molecular crystals was examined within the `pseudo-harmonic' phonon approximation. It was found that solitons could induce specific modifications of the speed of sound which shows a temperature dependence quite different to that in the case of the linear excitations. The possibility of an indirect experimental verification of the existence of solitons in molecular chains is suggested on the basis of these predictions.