I had this same questions a few years back when I wanted to add a sub to a old marantz integrated. This was recommended to me, I bought one but still haven't used it. At the time I had a pair of RB-5s but now I have Chorus IIs and they don't need a sub where I use them.
http://www.avrev.com/home-theater-accessories/accessories/outlaw-audio-icbm-1-integrated-controlled-bass-manager.html