Two days ago I posted my issue everywhere, including also the PlayStation Network Community forum. I posted my problem in the Italian section, and the English too, but I didn't get precise information about it.
In the last month I targeted the HDMI cable as faulty. I used a low quality cable, bought on an Ebay auction for a price just less than 6 Euros. Such cable unveiled its mediocrity, because of its excessive length - 3 meters long - and for its scarce shield: it wasn't even able to support the maximum native resolution between the digital devices, the well known "1080p".
In fact I set the PS3 to work with customized setup with my LED TV and I checked the basic resolutions 576p, 720p, and 1080i.
Last Wednesday my aunt Dolores gave me an high quality 3D certified HDMI cable by the German maker HAMA, an HDMI cable 1.5 meters long. I discovered immediately that the native 1080p resolutions is supported, without any strange artifact or interference. The shitty cable from Ebay - its seller stated it was a "top quality" cable - is really valueless, although the real guilty should be pointed to the cable length. If a cable is being stated as certified, its length shouldn't be a matter!
I tried again to probe the available resolutions and the 3D feature of my TV, but PS3 refused to detect it and I was going to say myself that it should be an incompatibility between my PS3 updated with firmware 3.55 and my LG 47LX6800.
The PS3 unluckily can't understand that the TV supports 3D view and it doesn't show such addictional page, where the PlayStation player can choose the extended 3D resolutions, 720p (3D) e 1080p (3D).
At last tonight I fixed the bogus by myself. One month ago I set the "Customized" setup in the video output settings and not the "Automatic" setup, after just replacing the shitty cable with the Hama one, and adding the 1080p resolution, in the list of the supported resolutions.
After changing from "Customized" to "Automatic" the extended 3D resolutions appeared as magic and even the bonus page, where you may tune the 3D display size in inches.
Some seconds later, I loaded one of the 3D Blurays from my aunt, the full Shrek collection in 3D and Monsters Vs Aliens 3D, all these movies are the cutting edge animation from movie industry, and the 3D playback run smoothly, with the TV dialog inviting me to wear the 3D active glasses.
Now we are playing with Granturismo 5 in 3D mode. More updated here in my blog in the next week...