It sounds like you were able to resolve the issue with getting your computer to recognize the devices for HDMI audio output by restarting the computer with the device connected via HDMI. This process often helps the computer detect and configure new audio playback devices correctly.
Setting the default playback device for HDMI audio is crucial for ensuring that sound is directed to the right output source, such as your new TV and sound system in this case. It's common for different devices to have specific settings that need to be adjusted to enable digital audio input and output.
If you ever encounter similar issues in the future or need further assistance with audio playback configuration on your Windows device, feel free to ask for...