Chilli, Any subwoofer that can match the volume you like to listen at will be fine. Most of us rarely listen over 95 dB and any pair of 12" subwoofers will do that easily. They all have adjustable gain. You just adjust it to match the output of your main speakers. It will require more power to reach the same volume but all the decent subwoofers are equipped to handle that. The 4 10" drivers you get with the swarm system will also do just fine.
So, unless you listen at 115 dB any decent subwoofer can be made to match your system. You are right to start minimally with two.
So, unless you listen at 115 dB any decent subwoofer can be made to match your system. You are right to start minimally with two.