Hi Dougal48, There is only one automatic shut-off setting on this product. When it is enabled the system powers off after sixteen minutes of inactivity (no sound coming from the system and no remote commands received.) To disable this:
On the remote control, press the System button
Press the down arrow to navigate to "AUTO OFF"
Press the left or right arrow to enable or disable the automatic off function
Press EXIT to exit the menu
If your system is shutting off mid-playback then this feature will have no effect on the problem. If that is the case then we will need to look at similar settings on your TV or other devices which could be triggering the system to turn off via HDMI CEC. Let us know!