We present a two-orbital extension of a previous cooperative vibronic Piepho-Krausz-Schatz model formerly designed for modeling the localization properties of molecular mixed-valence solids. The two-orbital extension involves a thermodynamic competition between electronic states characterized by different localizing properties. In addition to describing the "usual" second-order transitions between the low-temperature ordered phase (if present), and the high-temperature disordered phase, the present model also predicts first-order transitions, re-entrant phases and two-step transitions; discontinuous variations of the order parameter are associated with cross-overs of the electronic states. © 1994.