Thanks Saltgrass - not sure how to do this !! On 8.1 any attempt to manage audio devices brings up Realtek screen showing "Properties" as "Realtek High Definition Audio" but no sound on 2nd monitor still. No mention of HDMI in control panel audio screens. Default shown as 24 bits 48000Hz
If you have an HDMI output, it should show in the Playback Devices on the sound Panel. If you do not show anything, you may need a driver for that device.
You may need the HDMI cable plugged in to see the options. You are not sending sound anywhere else? You system may be able to deliver different sound from the front or back ports, but I don't think it can support two sound sources at the same time from the back.
New lead resolved sound issue but I have obviously done some unintentional alteration via the Control Panel as I now receive sound from e g BT Sport download but the picture on the second monitor is my wallpaper !! Help !!