Jason, the EP350 has a single line-level input to receive the output from the sub out on the receiver, so there's no need to consider the situation where a sub has both L and R inputs. One wire out, one wire in.
When a sub does have L and R inputs, either one can be used(they join inside)with a single wire. Both can be fed with a Y arrangement so that the two voltages make it easier for the sub amp to turn on(this is probably what you read), but it isn't essential since most receivers have plenty of voltage output even when only one sub input is fed.
