You use the preamp out on the amp to the preamp in on the sub. You can also use speaker out on the amp to the speaker level in on the sub. There are many different options depending on what sub you get. Here is the owners manual of the SVS sub that explains all the options on subwoofer hookup! BTW,what is your budget?
https://system.na1.netsuite.com/core/media/media.nl?id=69175&c=3634088&h=a2a627c5bd0810a8a24...
https://system.na1.netsuite.com/core/media/media.nl?id=69175&c=3634088&h=a2a627c5bd0810a8a24...