For sound you will need to use your optical out if you use the HDMI out from the PS3. There are some HDMI to DVI cables that also have a sound splitter and while harder to find will likely be your best option because I doubt your speakers have an optical input so then you are looking at another adapter to go from optical to rca/3.5 mm etc.
Your other option is to find a PS3 compatible headset. I have the turtle beaches that are wireless and have an optical input/output on the stand and they seem to work pretty well if not a bit overpriced. Good luck!!
Here is what it would look like: http://www.aztekcomputers.com/HDMIDVI6FTLOCK-GENERIC-3789846.html