Hi, and thanks for posting the link to the owner's manual - that made it much easier!
The connection for the sub is shown on page E-7 of the manual, and it appears that the speaker package comes with the necessary subwoofer cable (which is just an RCA cable). You don't need to use the splitter. You can connect the subwoofer output on your receiver to just one of the inputs on the sub (look at the manual for which one).