I contacted Samsung Support in the UK.
Samsung Support confirms that Kies is not compatible with Windows 8.1
Just to check, a rep installed Kies and tried to get it working, without success. Kies installs OK with its drivers but the PC never detects the phone being connected.
Do not waste your time trying to use Kies with a Samsung phone under Windows 8.1
Can Samsung give an outlook as to when a version that supports Windows 8.1 might be released?