Set the PS3 to "Multi-Audio Output" on the Audio Setting. The use the RCA AV cable that came with your PS3 and connect the White and RED to a AUX input of a speaker setup.
You can use a RCA to 3.5mm phono cable to adaptor to convert it to a 3.5mm headphone jack for speakers that just have a 3.5mm input for AUX audio. Or use a Digital optical cable and connect them that way if the speaker or audio device has one.
Or you could be as crazy as me with the audio setup:
HDMI> to HDTV/Monitor
RCA> 1000w Hifi system AUX input + adaptor for turtle beach headset.
Digital Optical> Sound Bar.
3 audio outputs to 4 different audio devices. I put this up just to show you how diverse you can have the audio setup on a PS3, any PS3 for that matter.