A modification of the statistical approach to the direct calculation of thermal rate constants [J. Chem. Phys 110, 88 (1998)] is presented. Within this approach, the trace in the flux-correlation function is evaluated by iterative diagonalization in the (strongly interacting) internal degrees of freedom and by a statistical sampling scheme in the (weekly interacting) rotational degrees of freedom. The wave packet dynamics is calculated employing the multiconfigurational time-dependent Hartree (MCTDH) approach. The O+HCl --> OH+Cl reaction is studied. This mixed approach is found to be more efficient and accurate than the purely statistical approach. The accuracy of the J-shifting approximation, the modified J-shifting approximation, and the K-conserving approximation is investigated in detail between 200 and 700 K.