Problems with sound whe conecting LCD with PC through HDMI

I have tried to use my LCD-TV as PC monitor and until now it was conected via VGA cable and worked fine. Also sound was no problem it was conected with standard 3.5mm audio cable. LCD-TV is Samsung LE32R72B with HDMI conection and on my PC (Vista Home) I have DVI conection and SigmaTel High Definition Codec sound card with 5x 3.5 mm conections for speakers.
I conected the PC and TV using HDMI cable with HDMI-DVI adaptor and picture is OK. But I don't have any sound on the TV. I tried to re-connect audio cables to DVI-IN Audio (on the TV), but it does not work. I used minijack-to-RCA audio cable as conection between TV (DVI audio IN) and PC sound card, but it does not work.
On the PC sound is on but nothing comes into the TV speakers. It seems that somehow HDMI/DVI conection has blocked soundcard and sound transfer.
If I chenged back to VGA cable and 3.5 mm audio cable, sound is back. I have read in forums that Sigmatel may have compatibility problems with Vista.
Does anyone have any idea how to solve this. Is there need for driver update or anything. I tried Vista driver update, but it says that all audio drivers are up to date.

What do Sigmatel say?

Do you mean Sigmatel support or Sigmatel hardware/software message?
I did not have any contact with Sigmatel support and on PC there is no error or hardware/software problems.
It is simply seems that no audio signal is going from PC to TV. I found in another forum one possible explanation. It could be that when HMDI cable is conected tha TV is tricked into "believing" that also audio signal is coming through the same cable. When in fact there is HDMI-DVI adapter on the other end and DVI is the source (which send only video signal) of the signal. Suggestion is to check if you can on the TV choose between digital and analog audio signal. Because by default it is possible that TV choses digital audio signal, so changing to analog signal should work (I still have to check this on my TV). So at the end it may not be a sound card or PC problem, but a TV issue.

Anyway it seems that in developers of the soundcards, graphic cards, TV and PC forgot about that HDMI and DVI do not carry same signal and are claiming that these two device should be compatible, but in fact it is a big mess.
Probably to get it to work I would need to buy new TV, new PC, new sound- and graphic card etc...
I will probably go back to VGA cable and continue as before and all this High Definition crap leave for another couple of years until they solve these issues.