If you're stuck with optical or coaxial SPDIF, then the only way to get 5.1 is through compressed audio, in which case DD Live would work well. PCM will be only 2 channels.
With HDMI, you no longer have that issue because new video cards can send out 7.1 uncompressed channels to your receiver.
Lone Industries L1: i7 3770, 2x4GB Mushkin Silverline, 512GB MX100, Dell U2412M + U2211H
Lian-Li A04: i5 2400, 2x4GB Mushkin Silverline, 160GB Intel 320, 4x3TB FlexRAID, all on Seasonic X460, hooked up to Sony 40" EX620 + KEF 2005.3 + Yamaha RX-V667