A:
Most current graphics cards support an HDMI output, but I personally don't know of any graphics cards that support an audio output. Graphics cards are specific for display, and do not transmit audio at all. HDMI supports video and audio in a single cable, but in this case with this DVI to HDMI cable, it's only audio since DVI is video only.
Most computers either already come pre equiped with a surround sound set up, usually 3 audio inputs on the back of the computer. Some people will go out and purchase an audio card to enhance their audio even more or when it comes to head phones, they'll come with USB sicks that have the drivers that run the head phones. Again, just because a graphics card (specicially for gaming) has an HDMI output, doesn't mean it supports an audio output. Hope that helps.