The multimode Brownian oscillator model of nonlinear response functions is generalized to include a multielectronic level system Interacting with several spectral densities representing solvent and vibrational coupling to electronic energies, transition dipoles, and permanent dipoles. Applications to resonant and off-resonant transient grating as well as to infrared and fifth-order Raman photon echoes illustrate how the various spectral densities may be probed separately.