Kef LS50 - can it handle a subwoofer properly?

I just got a pair of KEF LS50 speakers. As is known they are active speakers and I'm considering adding a subwoofer. They have facilities for a sub but what should I do regarding bass management?, they don't have an  amp, so no such feature, and I suspect the sub will just duplicate the lower frequencies from the speakers and I would like the proper function with the highs and mids on the KEFs and the sub  handling only the lower bass. Any solution greatly appreciated.