I tried to hook up my brother's SONY RPTV to his Time-Warner cable box via HDMI. It worked... for about 5 seconds and then intermittantly every 2-3 seconds. I went out and bought new HDMI cables thinking that I my have a defective set, same result. I then bought a cheap ($40) upconverting DVD player with HDMI output. It worked flawlessly. I called Time-Warner about the HDMI issue and they said (and I still cannot believe this!!!) they "provide the cable box, but do not provide support for HDMI users." This happened AFTER my brother switched from Direct TV at my request because the cable system gave him Hi-def HDMI at no additional monthly cost and equipment expense. That's what I get for trying to bring him into the audio/video revolution. Darn HDMI!!!
My comcast HDMI connection won't work properly with my HDMI receiver either.
It seems that cable companies are to blame... they aren't taking the time to design proper gear.