We actually have a Jawbone speaker box we use with it, but you can get all sorts of adapters that will split a typical headphone jack into RCA wires, etc. that you would, in turn, feed into a surround sound system.
I don't use the projector's audio out for my sound, I use my DVD recorder, which has video out and audio out jacks on it. Can also use a VCR as long as it has stero audio out puts. Hope this works for you.
I don't think you really want the inferior sound from a projector. An audio/video receiver will give you premium sound, and its only output will be to your projector, on which you will keep the sound turned off. This will make a great home theater.
You need to have a receiver that has an HDMI "in" and an HDMI "out". Pass your source (DirectTV, cable, roku, etc.) through your receiver and back out to the projector. I also put an HDMI splitter and an automatic switch on mine. When I turn on my Xbox, both my TV and the projector switch to the Xbox....shut it off and it goes back to Tivo. I have about 1000 hours on the projector. I still think it was a great purchase. The only thing I would do different is get an automatic screen. If you haven't purchased yet, get the ViewSonic PJD5523w instead of the 5133.
I have Boston surround speakers that I use with the projector. That plug looks like a headphone jack but if you look closely there are three separate portions on the shaft divided by an insulator. Output audio is much better than the projector. Some of the other responses may help you with the cable you need if your surround sound system does not have one. See flynoe's description.