How to use PS3 with a monitor?
Solution 1:
Do you still have the RCA composite + left/right audio output cable? (The one with the yellow, red and white plugs.) It is possible to configure the PS3 to output audio to both HDMI and the RCA cable.
Under "Settings" go to "Sound Settings" and turn on "Audio Multi-Output".
Solution 2:
You could try a device that separates the HDMI audio and video data with composite outputs, such as i answered in Help with sound for a Xbox 360 w/ HDMI cable