In this work a fully symmetrized quantum mechanical description of vibrational motion in terms of complex vibrational coordinates and complex basis wavefunctions is outlined, designed for studying vibrational level mixing and intramolecular vibrational energy redistribution (IVR) around CH stretch overtone states in benzene. Symmetrized local mode (LM) formalism has been applied to the CH stretch system, while the remaining benzene vibrations (including out-of-plane modes) were treated as normal modes (NM). Using the outlined approach a model calculation of the absorption spectrum of the first overtone state CH (n=2) at similar to 6000 cm(-1) has been carried out.