There's no option to disable the auto standby feature on this Soundbar. I currently have it connected through my PC through an optical connection and it is getting frustrating having to switch the Soundbar every time I don't have any audio playing on the PC for 20 minutes.
This wouldn't usually be problem since they expect you to use it with a TV.
European standards require the "auto off" feature to minimize power usuage. You could run some audio into it at low volumes from another app or browser window so it will stay on.