My son has a Onkyo HT-R391. This receiver has a passive sub. Uses One speaker wire 1 Positive ,1 Negative. I would like to upgrade his sub because I bought a new one. The sub I would like to add is a Energy 10.3 sub. I am not sure if I can do that and if so how I would wire it. Any thoughts? Thanks. Here is a pic of the Enery hookups