The HTPC Primer Page 3
New A/V components with HDMI pipe high-definition video and multichannel audio straight to receivers or TVs via a single, slender cable. Unfortunately, it doesn't work nearly as conveniently when hooking up a home theater PC. Most computers with HDMI only support video over that jack; unless the HDMI port is linked to both the graphics card and an S/PDIF header on the motherboard, it will only pipe out video.
Even if you can't send sound over it, HDMI is one of the best choices for hooking up your computer's video to your home theater. Many computers feature HDMI-out, and even ones that don't will almost always offer DVI-out. A DVI-to-HDMI adapter or cable will let you plug into your TV or receiver's HDMI port with ease.
Sound can be a bit trickier, especially if you want surround support. Virtually every computer available has a simple stereo-out mini-plug port. A mini-plug-to-RCA adapter is all you need to connect the system to your receiver. It's a simple solution, but it only outputs stereo. That's fine if you have a 2.1 system, but if you want to kick out the jams on 5.1 (and don't want to rely on in-receiver faux-surround processing), you'll need something else.
Many sound cards support surround and feature multichannel analog outputs. Each surround channel gets its own mini-plug port, for ease of hooking up PC surround speaker kits. If you don't mind a Gordian knot of cables connecting your PC to your home theater, a half dozen mini-plug to RCA adapters running into your receiver's analog input is enough to pump out the 5.1 goodness. There's a simpler way, though.
Higher end PC sound cards, like the Sound Blaster X-Fi Titanium series, feature TOSLink optical outputs. A single fiber optic cable is all you need for surround sound audio. These sound cards often support Dolby Digital and DTS formats, making them even more tempting if you want to use your system to play DVDs and Blu-ray Discs.
If you're using a media extender to send your media to your home theater instead of connecting a computer directly, things will probably be much simpler. Many media center extenders, including Apple TV and later model Xbox 360 systems, have fully functional (video and audio) HDMI ports that can handle sound and video.