The Manual suggests both but if you only have 1 subwoofer out on your Receiver I don't see why 2 would make a difference. If anything it will help with the auto on feature. Try 1 and see where that gets you.
Just to note, I use 1 on my Velodyne DPS-12 and everything works fine. The DPS-12 manual suggests using just the "L" input if the signal is coming from an LFE source (like your receiver source). They usually include 2 inputs if you have a pre-amp feeding the subwoofer with both a L and R output.
SheepStar