I would think passive ATC 50s which add ATC's famed midrange device and the "SL" 9 inch woofer with your current subs would be something to look into; might be a better comparison to the S8's than the 20's. The high crossover is at 3500 on the 50s, 2K on the S8's. The mid dome of the ATC's will offer best in class dispersion and off axis performance.
Brad
Brad