An attempt is made to improve the accuracy of a multi-channel parallel acousto-opticalspectrum analysis through involving an additional nonlinear conversion into dataprocessing. For this purpose we investigate the potential of exploiting a co-directionalcollinear wave heterodyning within an analysis of ultra-high-frequency radio-wave signals.The wave heterodyning under the proposal is performed via mixing the longitudinal elasticwaves of finite amplitudes. It leads to a two-cascade processing in the single-crystallinecell and makes it possible to improve the relative frequency resolution of theacousto-optical spectrum analysis by an order of magnitude at the same frequency range.Both the theoretical findings and the corresponding estimations were used inproof-of-principle experiments directed at creating a new type of acousto-optical cell. Thegeneral concept of the proposed method and the basic conclusions are confirmed byexperiments with the developed acousto-optic cell made of a lead molybdate crystal.