Hooking up an integrated to a subwoofer

Let me first say, I used to know how to do this, but have forgotten.

Im hooking up a friend’s NAD 320 to a subwoofer, Running it full range, so am NOT connecting the sub to the speakers (same manufacturer, Nola). I have two Audioquest Hard RCA splitters to use for the hookup. (1 male and 2 female ends on each splitter.

I have unplugged the bus bars that connect the "preamp out/amp in" settings, so now the preamp-outs are free. I have Y splitters (2), but I can’t remember the actual hookup. if I plug in the male part of the splitters - one into the right channel and one in the left - and run the right and left channels of the sub into the splitters, I will have one (female) RCA empty on the preamp end. What am I forgetting here?