The wireless kit uses the LFE input ( also called Co-ax, Digital Co-ax, Sub-woofer cable input, Raw input, etc.) but its basically a RCA cable (Red-White) combined into a high quality audio cable specifically for sub-woofers. Look on the back of your sub-woofer, it typically will have a (1) a standard power cable input, plug that into the wall (2) four pairs or more, wire terminals (red - black for positive and negative) these are just so you can wire your speakers to the sub-woofer and than to the receiver (don't use them) (3) a RCA, red and white input (first option to plug the sub-woofer into your receiver (4) A LFE input (best option) to plug into your receiver.

Only use either the RCA pair or the LFE input to connect the sub-woofer to the receiver (in the case of this kit use the LFE input to plug the sub-woofer into the box and the other box into your receiver) LFE is best because it doesn't use any filters built into your sub-woofer and instead uses the ones in your receiver which are much better.

The transmitter and receiver come with RCA cables, which should work fine. Look at the multiple pictures on the Best Buy website and you'll see the cable set-up and the included cables. These should work for over 90% of the speakers being used.

There are 2 ways you can hook this device up. The cheapest way would be to just hook up the single RCA plug to the right channel on the sub. The second way would be to get an RCA Y plug and feed both the L & R channels on your sub with the single output from the Rocketfish.

If your AV receiver has crossover management, which most have, you only need to use 1 cable and plug it into the socket labeled LFE. On my subwoofer, that's the left socket

It sounds like your sub only has line level inputs in which case this product unfortunately won't work. However, I find it rather odd that a powered subwoofer would only have line level inputs, have you triple checked to make sure the RCA input isn't hiding somewhere between dial etc. My sub has both line level inputs and RCA and the line level are quite a bit larger and easier to spot, especially because of the color difference for positive and negative inputs, since the RCA connectors address that for you, the RCA connector on my sub is all black and is very difficult to find, but it is there. I would double check the sub, if it is powered, it will most likely have an RCA input.