Preamp: Benchmark HPA4
Monoblocks: Parasound JC1
Sub: SVS PB-2000Pro
Are you using the XLR outputs on the HPA4 to the JC1s?
If you can use both XLR and RCA outputs simply use the RCA outputs to the subwoofer.
If you want to run speaker wire there are several ways.
Wire to sub and then to speakers, wire to speakers and then to sub, 2 wires from JC1, one to speakers and one to sub.
Do you have room for another subwoofer?
Run one from left channel and the other from the right channel.