You can use the sound bar in a 5.1 system by using it as the left and right front speakers since it is a two channel setup, but the end result would be awkward. You would use the Analogue RCA inputs on the sound bar, as this won't work with the digital inputs. The sub will work with this as well. If you wanted to build off it, you would want to buy an additional self-powered center speaker and some self-powered surround speakers. It would be awkward and furthermore, the center and sound bar would be timbre-mismatched, but if you aren't picky about sound quality, that won't be a big deal. You can also hook the sound bar to the center channel pre-amp output on a receiver that has that, but if you can afford a receiver with pre-amp outputs, you ought to be buying a better sound system to begin with.
Personally I would just start over again with the sound system.
If you just want decent, simple two channel sound, you can skip the receiver and just get some self-powered monitors like these:
While they would also be not so easy to stretch into a 5.1 system, they will sound a hell of a lot better than that sound bar, guaranteed. You can hood those up to your TV just like your sound bar. To get good bass from monitors like that, look for ones with larger woofers, around the 8" diameter area, like this:
Your sub wouldn't work with that setup. It looks like your sub will only work with your sound bar, sorry to say. To be sure about that, look at the back of it and tell me if there are any jacks there.
If you eventually want a good sounding 5.1 setup, the thing to do is buy a decent 5.1 receiver and some front stage speakers for a start. Then add the necessary components as you can afford them; a subwoofer, a center speaker, and surrounds. Try to have the center match the same set as your front right and left speaker. It isn't as important to have your surrounds match, and don't worry about matching your subwoofer, just get a good sub.