Did you assign the HDMI port? You need to assign it to a specific thing (Game, DVD, etc) or elese it wont work.
You manual will tell you how to do that,

Also, if you
did do that, then check the PS3s settings in the xmb.
Sound settings -> Audio Output seetings -> HDMI -> Automatic.
Good luck. Just so you know - when you get your 605 set up, its the greatest thing ever.