For some reason, there doesn't appear to be any cables available that offer any sort of audio output for HDMI/DVI conversion. I have no idea why, as there is no reason could couldn't have HDMI on one end, and DVI + Audio (3.5mm or component) on the other.
However, there are alternatives. There are component to DVI adapters, so you could run component cables out of the PS3 (or HDMI to component cables) and attache the component video to the DVI adapter, and the component audio to your audio output.