I have no experience with any of the equipment you're talking about.
That said, a couple of things come to mind. The PS3 might be outputting through the right port, but in a format that your receiver doesn't get along with. A higher bitrate, perhaps. DTS could be another possibility. I'm guessing you've already looked for such settings in the PS3, but you never know. You might also look for alternate modes in your receiver.
The other possibility is that newer PS3's might have activated some form of DRM, which was one of the big selling points of HDMI, IIRC. It's possible that if your receiver doesn't support the aforementioned DRM, then the PS3 won't output via HDMI. I know that a lot of satellite subscribers recently got hosed by this when their providers implemented a system not supported by their older DVR boxes. Pretty serious bullshit, frankly, but such is life nowadays.