I replaced my old Onkyo 7.1 system with this Vizio S4251. I had just installed the Vizio S3821 in the bedroom and it works great, so I thought the new one with rear surround sound wired to the wireless subwoofer would be a perfect replacement for the Onkyo. My rear surround speakers are mounted in the wall and are wired back behind the Vizio TV and blu-ray player. The small rear speakers that come with the S4251 are OK, but I did not want any wires, so I soldered the RCA connector adapters onto the ends of my speaker wires and plugged them into the Vizio wireless subwoofer that is placed in the front next to the soundbar. This makes a perfect installation. The sound is awesome and I do not miss the Onkyo at all. For those that have existing wired rear speakers, don't hesitate to hook them up to the subwoofer.
You can see the speaker wire stub-outs just above the subwoofer.