I say more the merrier. They add depth to my system. I started with one KEF R400B, Each sub has 2x10" speakers and a 200 watt internal amp. That was good, so I added a second of the same. I cross over at 40 hz. They are very adjustable, and you really don't know they're on, until you turn them off. My main speakers are Sonus Faber Cremona Ms. I'm contemplating adding a third.
