In 5.1 and 7.1 home theatre systems, the subwoofer is responsible for the bass. Unlike the satellites, the subwoofer is not connected via speaker cables but with an RCA cable, since it amplifies its signal itself in the - nowadays common - active design.
Information on connecting the T6 subwoofer with Teufel devices can be found here
Detailed information about connecting a subwoofer can be found on our YouTube channel - English subtitles are available, just make sure to turn them on!