As a natural extension for our recent work [SIAM J. Appl. Math., 73 (2013), pp. 2203-2223] we study pattern selection on a square lattice for longwave oscillatory Marangoni convection in a layer of binary liquid. In contrast to the previous studies dealing with weakly nonlinear dynamics of such systems only, in this recent work we developed a method based on the Fourier transform to describe the dynamics of finite-amplitude perturbations of both temperature and solute concentration. The method is then applied to study simple patterns on a rhombic lattice consisting of four or fewer interacting waves. The present paper is the first implementation of this theory to a problem with multiple interacting waves. In a wide range of parameters, alternating rolls (ARs) are the only stable pattern. For low values of the Schmidt number relevant for liquid semiconductors, a competition between ARs and traveling squares sets in and results in the emergence of a novel "asymmetric" pattern exhibiting properties of both traveling and standing regimes. Busse balloons for these patterns are found.