There should be devices in the Output Devices tab but there is no devices there.
Maybe it’s because your audio device was attached to sys-audio first and it’s not working after it was returned to dom0 when you shut sys-audio down.
Did you reboot the system after removing the sys-audio?
Also I don’t know which audio device do you use, there are three audio controllers in the Configuration tab but two of them are Off. Maybe you need to turn them on there.