Don't use the HDMI port from the graphics card.
The graphics card can process ONLY certain audio codecs like Dolby Digital. It's meant mainly for movies. It's generally quite pointless.
Unlike laptops, the HDMI audio is not connected in any way to your onboard sound, or sound card.
*The ONLY way to get proper audio is to use your onboard sound, or sound card. Unless you have a 3.5mm audio input on your monitor your out of luck.
I strongly recommend you get normal desktop speakers for far better sound and connect to the onboard sound or sound card.
My advice is the M-Audio AV30 desktop speakers for about $100. They have awesome sound for the price.