Unless you really need the deepest room shaking notes found on that occasional track or action movie sound track- a full range (or near full range) speaker driven by plenty of power is a better solution for me.
100 watts driving the main speakers just won't compete with subwoofer amplifiers of 500 to 1000 watts or more.
Drive your main speakers with 200 / 250 watts at 8-ohms and the need for a subwoofer greatly diminishes and becomes a better case set of compromises than even the best subwoofer setup.
You have $ to invest in a subwoofer system? invest in a bigger amp instead IMHO.
100 watts driving the main speakers just won't compete with subwoofer amplifiers of 500 to 1000 watts or more.
Drive your main speakers with 200 / 250 watts at 8-ohms and the need for a subwoofer greatly diminishes and becomes a better case set of compromises than even the best subwoofer setup.
You have $ to invest in a subwoofer system? invest in a bigger amp instead IMHO.