How to add subwoofer to my main speaker.

Assuming you can set the low-pass filter on the sub to an appropriately low setting, splitting the preamp signal is a reasonable way to go. With the 802's, the issue is not really relieving the main speakers of the low bass, but supplementing that bottom octave. What you don't need to do is use the subwoofer's high-pass filter, which could degrade the signal to the main speakers.

I don't have an SVS subwoofer but the specs and images on the manufacturer's site make it seem as if it has essentially the same options as my HSU subwoofer, with both low-level RCA inputs and high-level speaker cable inputs and outputs.

After trying all the options on my subwoofer, what worked best for me is to run a second set of speaker wires from the amp's speaker terminals to the high-level inputs of the subwoofer.

In other words, leave the speaker connections to your 802's exactly as they are now but run a second set of cables from the same amplifier speaker terminals to the subwoofer. I do it by using spade connectors on the main speaker cables and tapping into the back of the five-way speaker terminals with banana connectors for the subwoofer cables.

That method seemed to make it much easier to get a good, seamless integration with the main speakers, using the crossover and level controls on the subwoofer. The second set of speaker cables don't need to be of the same gauge or quality as your main cables, they're carrying very little power.

Again, I'm not sure this applies in your situation but it's worth a try if it looks as if it will work.