You can't use it like that.
Do you still have the original wires that came with the ps3?
You need to connect the audio Red/White out from ps3 to Aux in on the back of the soundbar.
Heres manual link,
You can still use hdmi for video if thats what you do.You will have to change audio output on the ps3 to Audio Input Connector / SCART / AV MULTI
Then to hear sound from ps3 change soundbar to Aux.