As long as the amp you get has HDMI inputs that can strip audio information (and aren't just pass-throughs), the PS3 can deliver HD sound as Linear PCM. This is currently the only way to get the new audio codecs from PS3 to receiver, since, as moomin says, the PS3 has no multichannel analogue outputs.
And I have to reiterate what you said about the sound on Blu-ray discs, moomin - I'm using an optical cable to bitstream to my Onkyo system, and the difference between the simple DD/DTS soundtracks on Blu-ray and standard DVDs truly amazed me! DVDs sound decent, but BDs sound much better - watching my current favourite BD (Batman Begins - absolutely awesome, although I'm counting down the days until The Dark Knight), I never fail to grin when the Batmobile tears through my living room, and this is just the Dolby Digital track! I honestly can't imagine the TrueHD track being that much clearer or punchier than this - to my ears, it's just fabulous!