Based on the Chen--Moller--Sauvaget formula, we apply the theory of integrable systems to derive three equations for the generating series of the Masur--Veech volumes ${rm Vol} , mathcal{Q}_{g,n}$ associated with the principal strata of the moduli spaces of quadratic differentials, and propose refinements of the conjectural formulas given in [12,4] for the large genus asymptotics of ${rm Vol} , mathcal{Q}_{g,n}$ and of the associated area Siegel--Veech constants.