We develop an advanced approach to the optical spectrometer with acousto-optical dynamic grating for the Guillermo Haro astrophysical observatory (Mexico). The progress consists in two principal novelties. First one is using the acousto-optical nonlinearity of two-phonon light scattering in crystals with linear acoustic losses. This advanced regime of light scattering exhibits recently revealed additional degree of freedom, which allows tuning the frequency of elastic waves and admits the nonlinear apodization improving the dynamic range. The second novelty is combining the cross-disperser with acousto-optical processing. Similar pioneer step gives us an opportunity to operate over all the visible range in parallel regime with maximal achievable resolution. The observation window of optical spectrometer in that observatory is ~9 cm, so that the theoretical estimations of maximal performances for a low-loss LiNbO3-crystal for this optical aperture at λ = 405 nm give the spectral resolution 0.0523 Å, resolving power 77,400, and number of spots 57,500. The illustrative proof-of-principle experiments with 6-cm LiNbO3-crystal have been performed.