You can use the High Level (speaker) connections. Should be indicated in your subwoofer instruction's manual on how to do the proper connections.
If you don't have the manual, just downloaded it from the Focal sub web site.
* For proper High Level connections from speaker cables, look in this thread from post #3
(up to post #6), of this link:
@
http://www.audioholics.com/forums/showthread.php?t=57364
** It's a short thread, you might is well read it all, to get acquinted with the various methods of connections. But in your case, the easiest and FREE, is the High level one (from the speaker cables: from the back of your amp, to the back of your sub, and to your speakers).
Cheers,
Bob