Laptop troubleshooting forum: No Sound: HP HDX Laptop to Phillips HD TV

I have:
An American HP HDX16 Notebook PC running 64-bit Windows Vista. with:
NVIDIA GeForce GT 130M video processor
Intel Mobile Core 2 Duo P7550 processor

I'm trying to hook up to a British Phillips HD Flatscreen television, model: 26pfl5522d/05

I can get the video to connect and it looks beautiful, but the audio insists on continuing to play via my laptop. When I open the sound interface in preferences it indicates that there is no HDMI audio output plugged in. I've tried disabling my normal audio playback devices, restarting my laptop with the telly connected and activating various media players to see if anything makes it kick in.

I know the problem isn't the telly or laptop individually as I was able to fully connect the laptop to a (newer model) Toshiba telly in the USA, and the telly runs both the Xbox 360 and the bluray player via HDMI without problem.

Can anyone tell me if this is possibly a compatibility issue between the telly and laptop that will prevent me from ever playing audio via the telly? I've checked for updated NVIDIA drivers, I have the the most recent ones produced before they stopped supporting this card model as far as I can see.

What's really frustrating is that I'm certain after playing about with settings for a couple of hours a year or so ago I was able to get audio to play through the telly (if I recall correctly I could only get Windows Media Player's audio to carry over, but that was something at least). Unfortunately I didn't attempt to make the connection again for months and all successive attempts since have failed to produce audio.

There was also an attempt to connect an American MacbookAir to the telly a couple of months ago, which also failed to produce audio via the telly.

Any tips or suggestions, or even a "this isn't possible" so I know to stop digging through forums looking for a solution, would be appreciated.

Also, as a note, I don't have a British HDMI capable laptop available to try hooking up to see if it is as simple as an American/British compatibility issue.