Many use subs with their Spatial Audio speakers (I have M3TMs) because they are driving the speakers with small tube amps. But I find my pair of GR Research OB subs improve the bass of every speaker I have tried them with. Mind you, I haven't been using huge megabuck speakers that shake the earth by themselves. But yesterday with a 70 watt tube amp on the spkrs and the subs engaged, I played Queen's We Will Rock You so loud I may have foundation damage.