For everyone who is having HDTV display and digital audio output problems take the advice of a few of the other posters here and go out and purchase Gefen HDMI Detective Plus. It retails for $129 but Amazon has it for sale for around $80. It will fix your Mac HDMI out video and audio problems period. Yeah it ***** you have to buy it but if you have the HDMI problems it was designed to fix you already have spent several thousand dollars on computer and home theater equipment so what is another $80 to keep everything working right.
By way of background, I have a late 2010 Quadcore I7 Imac, which also doubles as a HTPC for a 7.1 speaker set up in my loft with my Denon 4308CI amp and Panasonic HDTV (via a long 100 ft HDMI run). I use the Imac bluetooth keyboard and trackpad in the living room to control the Imac when viewing on my HDTV. The set up worked great with Snow Leopard until the 10.6.8 update killed my digital audio. I reverted to 10.6.7 to fix the issue until Lion 10.7.1 was released and I read on another Apple thread that the HDMI out issues had been solved. When I upgraded I lost both HDMI video and audio and I was hoping that 10.7.2 would solve the issues but it did not.
Anyhow, I was getting ready to go back to 10.6.7 again but read this whole thread for solutions and stumbled on the Gefen hardware solution. After doing some research it seems that many HTPCs have HDMI out problems with software updates and AV receivers and not just Apple. I bought the product, spoke to Gefen tech support before the set up as their instrucitons are a little unclear but after that I set up the product in no time and now everything is working perfectly once again. Best of all, I don't have to worry now about future software updates killing my HDMI out video and audio again.
BTW, if you use a AV receiver with your Imac just use one of the preset Gefen generic codes at set up as storing your HDTV's EDID in the Gefen may not allow you to push multi channel digital audio as well as video from your Imac.