This study introduces a compressible diffuse interface method to treat flow dynamics for regimes ranging from subcritical two-phase flows to supercritical flows. The model relies on a cubic equation of state to take advantage of its wide domain of validity. This choice requires a careful treatment in areas where the fluid state lies in the binodal region. In this case, thermodynamic equilibrium is computed, yielding a two-phase stable fluid state. The model can be related to the family of multifluid methods such as Baer and Nunziato's 7-equation model (1986), considering speed, mechanical, thermal and thermodynamic relaxations. The model is integrated in the AVBP solver, jointly developed by CERFACS and IFPEN. This paper details the modified thermodynamics and derivation of the consistent boundary conditions and numerical schemes. Numerical validations are finally provided.