ASUS X72JK : using HDMI, the TV does not reproduce the sounds.

When I plug my laptop (Asus X72JK) on a TV via an HDMI cable, I have no sound coming from the TV (It worked my previous laptop, Acer). My computer produces good sound through its own speakers, but it is not relayed on the TV (which displays the same image as my PC).

When I look in the settings I see this:
- Control Panel / Hardware and Sound / Manage Audio Devices / Playback tab / "ATI HDMI OUPUT: Not Connected".

Please would you have a solution?

Configuration:
- PC: Asus X72JK-TY004V
- TV: Sony KDL-46W5500 ref
- OS: Windows 7 64-bit original.
GPU: ATI Mobility Radeon HD 5145 (driver v8.14.1.6091), ATI High Definition Audio Device (v5.0.7000.9).
Audio: IDT High Definition Audio CODEC (driver v6.10.6259.0).

Already tried:
- Different softwares (VLC, Windows Media Player, web browser on Dailymotion).
- TV off / on again, PC off / on again, restart PC.
- Tempted to activate the "ATI HDMI OUTPUT": This option is not available in the menu (mouse right button).
- Look in "Device Manager" if a symbol of anomaly appears: nothing to report.


Notes:
- The drivers are original versions.
- On the Web English I read that other users of laptops from different manufacturers (eg Dell), but with an ATI graphics card HDMI had the same problem.
- This TV and the HDMI cable has already worked with Acer Aspire 5738ZG-434G32 (GPU ATI Mobility Radeon HD 4570), however the sound output does not always work, restarting the PC that solved the trouble.

I can't because this choice is greyed (because the device is reported as "not connected".)

Thank you for trying, qhn.

Nice idea. Unfortunately, the options I found with your help, did not display some more devices.

Path followed :
- Control Panel / Hardware and Sound / Manage Audio Devices / Playback tab / mouse right click in the white area of the window / enable "Display disabled devices" and "Display disconnected devices".

I did it (new driver installed : "ATI HDMI Audio" v6.0.1.6409 28/08/2011).
Unfortunately the problem is the same.

I had the idea to test my computer on a second TV (Toshiba 26EL833G) with the same cable, and the sound output is OK ! (The HDMI audio devices were automatically enabled).
So I think the issue is related to the Sony TV, perhaps since I did a firmware update 3 months ago (from version 1.730EA to 1.741EA).

I will write to Sony support, and try to get a older firmware file.

Thank you for your help.