I hope this will be of some help to others.
I recently purchased a HP slimline desktop s5150t with ATI Radeon HD 4350 video card. After I got everything setup, I noticed that I only had 2 channel audio (stereo) on my Receiver connected to the PC using HDMI. I checked the HDMI Audio Device driver and found out that it is an outdated driver from Microsoft. I tried to update it, the system responded saying I have the latest updated driver. I called HP Tech Support, after spending an hour on the phone I was disappointed to come out with nothing. I continued my search on various forums and ended up in the RealTek website. After trying many drivers I found the driver ATI HDMI Audio Device R2.35 2009/10/12 17370k, I installed it and got everything working. That was a big relief Now I get DTS & Dolby sound output through the HDMI cable on my receiver
Once you are on the Realtek home page, Click on Downloads and then choose High Definition Audio Codecs (Software) and Download the driver ATI HDMI Audio Device R2.35 2009/10/12 17370k