A quick look on the web at your amp manual - it says 'A subwoofer with a built-in power amplifier can be connected to be used.
Connect LINE INPUT on the subwoofer with a built-in power amplifier to PRE OUT: SUBWOOFER terminal on the integrated amplifier.
If your subwoofer does not have a built-in amplifier, connect the input jack of your amplifier to the pre out jack of the subwoofer.
For details, refer to the manual supplied with your subwoofer.