Hi kfalls.
Note that the PS3 can only pass on the high def audio once it has decoded them internally; it cannot pass on the bitstream package to the amp for it to decode. It will pass on the separate decoded channels as (L)PCM channels (your amp might call it Multi PCM channel or similar).
These make up the High Def Audio signal.
On the PS3 in the BD/DVD settings make sure audio output is via HDMI and that you select LPCM NOT bitstream.
In the Soundsettings choose Audio Out on the PS3 (oddly in a different settings menu) you can tick all the audio formats you want the PS3 to handle - tick all the ones you want and according to your set up.
On your amp, go into the Audio option of the Settings menu and find HDMI IN and set to Auto. Apparently PCM signals will be given priority but if a High def audio isn't present it will automatically see ordinary DD or DTS 5.1.