  A recently developed theory for the problem of Andreev reflection between a
normal metal (N) and a multiband superconductor (MBS) assumes that the incident
wave from the normal metal is coherently transmitted through several bands
inside the superconductor. Such splitting of the probability amplitude into
several channels is the analogue of a quantum waveguide. Thus, the appropriate
matching conditions for the wave function at the N/MBS interface are derived
from an extension of quantum waveguide theory. Interference effects between the
transmitted waves inside the superconductor manifest themselves in the
conductance. We provide results for a FeAs superconductor, in the framework of
a recently proposed effective two-band model and two recently proposed gap
symmetries: in the sign-reversed s-wave ($\Delta\cos(k_x)\cos(k_y)$) scenario
resonant transmission through surface Andreev bound states (ABS) at nonzero
energy is found as well as destructive interference effects that produce zeros
in the conductance; in the extended s-wave ($\Delta[\cos(k_x)+\cos(k_y)]$)
scenario no ABS at finite energy are found.
