Sure, Allan; as others have pointed out, you're in control of the volume at which a sub is playing. The idea really should be that you don't notice the sub as a separate sound source, rather it's as if the speakers were putting out more bass on their own.

For most music(pipe organ being one of the exceptions)more bass than the M80s are capable of isn't needed. Some LFE effects in movies do extend deeper however, and capable subs are a substantial improvement.

-----------------------------------

Enjoy the music, not the equipment.