In this work we study from a theoretical point of view microcavities embedding organic materials featuring vibronic progressions. As already shown in seminal experiments, the presence of vibronic replicas largely enriches the physics of such systems with the appearance of new polariton dispersion branches. We calculate the linear optical properties of such microcavities using two distinct models, quantum the first, macroscopic the latter, which are fully consistent with each another. They are shown to describe the strong-coupling regime in very good agreement with the available experimental data, using independently determined material parameters.