Question about hooking up a subwoofer to home theater receiver?

I think you may be a bit confused. You say no LFE input, yet you claim to be using the LFE input (That's what the RCA jacks are!).

As to whether to use a Y adapter / splitter or not advice varies. I'd follow the sub manufacturer's advice if available.

The first link claims: "You'll want to use a Y-Adapter to combine the two (left-white & right-red) RCA jacks on the Subwoofer into one. They are labeled “Left and Right Line-In Inputs”, but for a typical home theater, you only have one cable coming from the receiver to the Subwoofer. If you don't have one or don't want to get one, you don't need the Y-Adapter; just use the left or right input by itself. Some prefer using the Y-Adapters because it makes the auto-on/off switching more efficient on some Subwoofers."

Another says there are some subs with dual amps .. in which case you need a Y-adapter.

Others claim that in most cases you can use either input alone.

See the 2nd link for a good overview of how to set up a sub. Note that if you use the receiver for bass management be sure to set the sub crossover to the highest frequency (or to "bypass" if available).

Powered Subwoofer With Lfe

get a 1 to 2 rca splitter and plug into left and right, thats how most subs are, well at least my jbl is and the manual says to use a splitter, or you can just use the left