Hi, 2010 Mac Pros support audio via Display Port, even using a DP to HDMI adapter (with a compatible monitor/TV). I wonder if older Mac Pros equipped with 5770/5870 cards support this as well. To check this, just look up the System Profiler at the Hardware > Audio(built-in) section and see if HDMI/Display Port is listed at the bottom. Be sure that your System is set to English, as the panel is messed in other languages (at least German and French). Please, report whether you see HDMI/DP listed, your Mac Pro and Radeon model (and whether it's an Apple or flashed card). Thanks.