What worked for me is:
- Search: Sound: Settings
- Go to the desktop Sound app.
- Click on the device, properties
- Advanced tab
- -unclick "allow applications to take exclusive control of this device"-
- You will have to to this for all your devices as they are on
This also prevents windows 8 from lowering sound when you open up another app (e.g. Skype), so may be slightly annoying in some instances, but at least music continues as screen goes black after 2 min!