On my HTPC build I use an ATI Radeon HD 5450 and it can output surround sound over HDMI from games. I don't play a lot of games on this box for obvious reasons but those which will run give me full surround sound.
I don't know if they use Dolby Digital Live, I seem to get MCH PCM 5.1 displayed on the receiver instead of DD 5.1. It works fine though and all six channels work as they should with true positional sound.