For a four-stream approximation of the kinetic model of radiative transfer wih isotropic scattering, a numerical scheme endowed with both truly-2D well-balanced and diffusive asymptotic-preserving properties is derived, in the same spirit as what was done in [14] in the 1D case. Building on former results of Birkhoff and Abu-Shumays, [4], it is possible to express 2D kinetic steady-states by means of harmonic polynomials, and this allows to build a scattering Smatrix yielding a time-marching scheme. Such a S-matrix can be decomposed, as in [15], so as to deduce another scheme, well-suited for a diffusive approximation of the kinetic model, for which rigorous convergence can be proved. Challenging benchmarks are also displayed on coarse grids.