Here's what the manual says on page 4:
Hook-up (see fig. 1). There are a variety of ways to configure your
new sub. Usually, a simple mono, shielded 75 Ohm A/V RCA type
cable is used to take the subwoofer output of your DD/DTS
surround sound receiver and feed the low-level input of the sub's
amp. There is no need to "split" the signal going to the sub (c.). You
can feed either one of the two amp inputs, it doesn't matter, right or left.
The receivers you're looking at with two sub outs (if mono, as in not L & R) are designed to feed two separate subs. Depending on make and model, the receiver is either implementing an internal splitter of the same signal, or is actually independent of each other which can be processed separately for room correction.
SV oofers