Thanks for making your own thread on this. It should make it easier to keep track of things.
If you get a receiver like that, you'll need to get new speakers too. I suppose there might me some way to cut up your existing logitech x-530 set so the speakers are powered by the receiver, but that would not be recommended.
For a really cheap receiver like that, you'd probably only want to run audio to it.
That means that the video from all your sources would be routed directly to the display. Each audio source would then get its audio connected to the receiver with a separate cable.
For example with your PS3, you'd run HDMI from the PS3 to your display for video. You'd run a digital optical (toslink) cable from the PS3 to your receiver for audio.
The receiver would then power the passive speakers attached to it and send a signal out to a powered subwoofer.
To get true surround sound from a variety of sources, a receiver is the best way to go unless you have a set of computer speakers with several inputs that allow for surround sound. The Logitech z-5500s for example can accept surround sound from analog inputs (like a normal set of computer speakers), but also have two additional digital inputs that would allow you to connect a PS3 and other more HT related sources.
If you get a bunch of good deals on craigslist, you could get a decent receiver, 5 speakers, and a subwoofer (together or as separate purchases) for a few hundred dollars.
I don't think there's a single good $100 option that's going to allow you to keep using your x-530s in the manner you want to.
There are some products out there that allow additional connectivity to computer speakers, but I think it's hard to find them now and they tend to be high priced due to scarcity.
(Like the creative ddts-100 for example)
http://www.amazon.com/CreativeLabs-C.../dp/B00013JUA2
