Were having problem getting the sound from the Surface Pro 3 to my TV through HDMI. It worked before upgrading so Windows 10 had a different behavior. Found this http://answers.microsoft.com/en-us/surface/forum/surfpro3-surfusingwin10/no-hdmi-sound-after-upgrade-to-windows-10/45c740da-5326-48a1-9be5-1e84dca50ae8 on the internet, though it might be good to write down so I'll remember next time.
Right click on the speaker icon, on the task bar.
Choose Playback Devices.
Right Click the TV item in the list
Click the "Advanced" tab in the dialog
change the default format for audio playback to a lower value.