<p>Symmetric product orbifolds provide a controlled environment to explore generic features of gauge theory and holography. The tractability of these theories lies in the complete characterisation of their gauge structure through holomorphic covering maps. In this paper, we introduce a novel class of generalised covering maps, which define a universal family of interfaces between symmetric product orbifolds. These interfaces coincide with the holographic interfaces that were recently proposed as duals to AdS₂ branes in pure NSNS AdS₃ backgrounds. The new covering-map description enables efficient evaluation of interface correlators via a generalisation of the Lunin-Mathur method. To organise these computations, we derive a generalised Riemann-Hurwitz formula for interface coverings and introduce novel diagrammatic rules that systematically classify these maps. The new framework allows us to define a concrete grand-canonical ensemble that has the correct properties to compute correlation functions dual to open string scattering amplitudes. Using the generalised Riemann-Hurwitz formula, we explicitly show that the correlators of the ensemble structurally match string perturbation theory to all orders in the string coupling.</p>