Monoprice is proud to be among the first to offer a direct connect solution for connecting your Mac to your HDMI equipped HDTV.
Unfortunately that Apple employee is an embarrassment to Apple. They have no idea about which they are recommending to Apple's customers. That cable is uni-directional. It only works in the direction of mini-DisplayPort to HDMI. It is useful to attach a display or projector with HDMI input ports to a device that outputs through a mini-DisplayPort, such as your iMac.
To use the iMac as a display for the PS3 you will need a converter to convert the PS3's HDMI video signal to m-DP video signaling. Those currently sell around US$150.00 by developers such as Atlona and Kanex. They are also restricted to a video resolution of 720p.
If you want full 1080p resolution Atlona sells an HDMI to m-DP video scaler for around US$280.00.
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