humm, I don't know how to explain better.
in your PS3 video menu, you can select the outputs (hdmi, component, etc.), there's an option to enable dual output.
If you do, it will tell you that Stereo is forced in this mode.
Now both Video connectors (hdmi and component) will output sound simultaneously.
I'm using this "dual output" mode because I use hdmi to get better video on TV, and component to get better audio on PC.
If you don't use hdmi, you don't need the dual output mode. just select component.
How do you want to output your video ? hdmi on monitor or video capture card on computer?
digital hdmi port -> hdmi cable -> TV (or on your monitor's HDMI)
analog video port ->
component cable or
composite cable -> L/R cable connected to
RCA to jack adapter -> jack adapter connected to Line-in on PC.
Open the audio mixer on windows, go to recording devices and select line-in as input. (instead of mic-in, or something else).
instead of component or composite cable, you can also use a
RGB cable with audio output +
this one.