The acoustic diffusion equation model has shown to be a versatile alternative model for certain types of scenarios where the classical geometrical methods have been demonstrated to be inefficient or even inaccurate. In certain scenarios, the transmission loss plays a fundamental role for accounting, i.e., noise levels and sound propagation between rooms. This paper presents an extension of the absorption boundary conditions known as modified that unifies previously proposed boundary conditions in one equation, including transmission of energy between coupled rooms by both openings and enclosures.