Hello. My name is Michael. I can help you with your question.
The RCA jacks that you have on the back of that projector for audio are for INPUT only. They will not output through those to external speakers. There are other connections on the projector for output - the 3.5 inch analog is an output.
More commonly, however, the source of the video (like DVD or set-top box) would be used to directly output audio to the external speakers. In fact, that is what I would recommend. This way you will be controlling the audio from the source, which is the correct way to do it.
Let me know if you still have questions.