I'm not sure this is an ATI issue. I'm inclined to believe this is how HDMI works. HDMI is a video and sound adapter, it may not work any other way.
However, there is possibly one more thing to try. If you right click the sound icon on your taskbar, hit click playback device, you are normally able to choose your Realtek audio, or the speakers it's hooked up to.
i tried this and everything elese i could imagine including an unnecessary Windows 7 reinstall, what i wasnt able to think off prior to a reinstall was using my DVI-HDMI cable
when using in Playback it shows Realtek HDMI Output/ATI HDMI Audio as Unplugged since im using a DV-HDMI connection, and Realtek High Definition audio works fine, but when i use HDMI-HDMI even if ATI HDMI Audio is disabled no sound comes out even if i select Realtek High Def audio and you can clearly see the volume meter go up and down indicating that its working but just no output
anyway ive fixed it but am still baffled as to why they work the way they do