Get a seperate DAC, most will have an optical input and a lot will have rca out. The Musical Fidelity X-dac v3 provides you with these features, but I don't know what your budget is.
A seperate dac will provide you with better sound on 16 bit, in stereo. I am not sure how to get everything streaming from the optical link in stereo, but for a lot of applications it will probably be very straightforward. Maybe Nrostov can help you with that, I don't own a ps3, or maybe you know.