Inspired by a fair amount of experimental and theoretical works describing nonlinear transport in hybrid mesoscopic structures, we study a confined state coupled to different types of noninteracting leads. It is shown that specific properties of the electron bath, here simulated by the presence of van Hove singularities in the spectral density of the reservoirs, determine sharp resonances in the differential conductance at finite applied voltages. For both magnetic and nonmagnetic single impurities, the two-channel network exhibits a resonant negative differential conductance behavior in a region of parameters which is not expected for ideal electrodes. This result may have important ramifications in probing resonant tunneling experiments. (C) 2004 American Institute of Physics.