The obvious choice would be the ATC C1 subwoofer if you want to keep the same tight, controlled, and clean bass that the SCM11's produce. Do you have a budget you're sticking to?
nokz:ok so im running my ATCsc11S THROUGH AN ASTINTREW AMP WHATS THE BEST SUB FOR THESE SPEAKERS
Hi nokz
I have already recommended the C1 sub to you in the Home Cinema section. In case you are not aware there is also currently a similar thread in the Home Cinema section (started by AlmaataKZ) which you also might find useful