In order to get back "Play To", restart DeviceAssociationService.
For more convenience, run a batch file with admin permissions:
net stop "DeviceAssociationService"
ping 127.0.0.1 -n 1
net start "DeviceAssociationService"
What works: After boot, I see wmpdmc.exe running in Taskmanager. In Windows Media Player and in Windows Explorer, right click on music files brings up the command "Play To". It opens a "Play To" window with a playlist and control buttons for playing music in my wifi box.
What fails: When the...