It shouldn't matter at that cable length as long as it has reasonable shielding, but if you had the connector at the receiver/processor output I would go with balanced connections to be sure.
If you don't have a display to see FR (like with an SMS-1 for example) set your RS metre at your favourite seat and try all the phase switch combinations. Many articles suggest, erroneously in my view, to choose the setting which sounds loudest. Loudest often means bigger peaks. Its far better to choose the combo that has less volatility on the metre when running a sweep. That means a smoother FR. The beauty of multiple subs is all the headroom you have to raise the volume and keep things smoother and clean.
