Garcianc2003's comment about turning the sub off in the receiver or processor is assuming that you use the Y adapters to send copies of the left and right front channels to the sub - it does not apply in the case of splitting the subwoofer output and connecting it to both inputs on the sub.

I've simply connected to the left input on both my old sub (SVS 25-31 PCi) and my current sub (LFM-1).