You can connect a REL between the integrated and your speakers using their preferred and proprietary high level (speaker) cable. After an in home comparison the REL is literally the last subwoofer I'd ever choose. But hey, they have their following, mostly their only subwoofer experience.
You can connect most any subwoofer from the single (summed) subwoofer low line level (RCA) output of your integrated to the subs corresponding RCA input. Or...
http://syzygyacoustics.com
You can connect most any subwoofer from the single (summed) subwoofer low line level (RCA) output of your integrated to the subs corresponding RCA input. Or...
http://syzygyacoustics.com