The checksum of Fusion6.dmg was correct, the manually uninstalling of Fusion 5 according KB1017838 runs and the following Install of Fusion 6 was successful.
But my Windows 8 Pro under Fusion 5 was running fast, under Fusion 6 Windows 8 is a lame duck.
So I´m not happy about Fusion 6.
But many thanks for your help!