The separation of homodyne and heterodyne signal components is discussed for the transient grating technique of thermal diffusion forced Rayleigh scattering (TDFRS) on binary liquid mixtures and solutions. Utilizing the unlimited repeatibility and the presence of a fast thermal signal component, a phase stabilization technique is implemented, where the phase information is obtained directly from the diffracted signal. In terms of sensitivity and robustness against perturbations and experimental imperfections, the heterodyne detection scheme shows clear advantages, and both the theoretical signal amplitudes and the shot noise limit are almost reached. For experimental constraints, like sample heating and convection, quantitative expressions are obtained, and formulas are derived to predict the optimum cuvette thickness and grating constant and the achievable signal-to-noise ratio for any given sample.