I use one HDMI and one Display Port (with a DP to HDMI cable) to connect my graphic card (HD 6950) to a TV and an AV Receiver. If both devices are connected, the HDMI Audio Driver (newest version) seems to select the HDMI port for audio playback and I figured out no solution in Windows 10 to switch the audio output to the device connected with the Display port. If I tell the Catalyst driver to use only the device connected with Display Port, AMD HDMI Output says "not connected" and a red sign is shown beside the speaker symbol in taskbar.
I can rule out issues relating the TV and the AV-Receiver as both of them work if I switch cables.
If only the DP to HDMI cable is plugged in I also get sound with the DP-Port. If I hot-plug the HDMI cable the exact same problem occurs with the device connected to the HDMI port and I found out no solution to play the audio over HDMI.
HDMI and DP connected: Audioplayback works only with HDMI
only DP connected: Audioplayback works with DP
only HDMI connected: Audioplayback works with HDMI
startup Windows with DP, hotplug HDMI then: Audiplayback works only with DP
In Catalyst there's no option to select audio devices. I already completely deleted and reinstalled the catalyst driver. I also tried the separate Realtek HDMI Drivers. Video playback works as it should in every setting.