In this study we present an implementation of a coupled multiscale quantum mechanics/molecular mechanics approach well suited for studying compositionally rich extended defects. Our focus is on interfacial phenomena of α2/γ phase boundaries in intermetallic TiAl alloys. We prove that our implementation is capable of accurately reproducing site-preference energies of solutes reported by previous density functional theory studies. To properly study segregation phenomena, we developed a formalism for segregation energies in systems with two sublattices (Ti and Al). Our model provides predictions consistent with atom probe tomography measurements reported in literature for a large number of solute atoms.