Two other possibilities include firmware issues w/ cable box & HDMI handshake issues between cable box & Onkyo receiver. You also quite possibly have a defective receiver. (Are you still under warranty, btw?) I'd put power supply on the very bottom compared to these, since the other possiblities are not at all uncommon if you do some reading. Try over at AVS forum for more discussion on this stuff. Sorry I don't have any specific experience with your exact models to give you quick fix.

Keep in mind only the expanded Blu Ray audio will benefit from the surround sound processing on the receiver via HDMI. Your cable box (which brand/model, btw?) only outputs DD5.1 and none of the wideband audio codecs, so you could still get surround sound by running a separate digital optical out into the Onkyo, at least until you find a solution which permits you to utilize only HDMI connections. So basically, the HDTV acts as a monitor like it should.

I don't own a PS3, so I dont' know if you could also split the audio/video like you can with a typical Cable box. Many folks don't run all HDMI to the receivers, FWIW.