In the framework of a recently proposed approximation, we investigate here the frequency spectra of two-band fluids (fluids composed of particles with two independent Drude oscillators embedded) as well as fluid mixtures of particles with one Drude oscillator. Both cases are analyzed in the low density regime where departures from the linear theories are more evident. Our theory, which goes beyond the mean spherical approximation (MSA), reproduces the correct low density spectra while retaining the proper qualitative behavior of the MSA at fluid densities.