I have 12" dual subs, F12s from Rythmick and they work flawlessly with my PBN Montana XPS speakers which are 4 ohms. Plenty enough bass with the right amount of slam and definition.
However, FYI, to obtain a non overly booming sound they had to be placed on opposite walls as you can see in my system. When they were placed by the speakers I would have this huge earth shaking tremor in the rear of the room. Just pointing it out because you say you have space issues for subs placement.