I tested this a few times last week stepping through each upgrade from 8.1 up to Win10 AU on MBR and UEFI systems and I updated the KB last Tuesday to make the steps clearer. I kicked off a test earlier today from Win7SP1x64 Enterprise directly to Win10x64 AU Enterprise and it upgraded successfully.
When you were running the script, it should take about 10 minutes. Do you happen to have saved the output of the script? Where is the \DVD directory located; on a network share, USB, or the local drive? I have tested on USB and network share successfully; I don't believe it will work on the local drive. If you are upgrading to Windows 10 Aniversary Update you must be running MDE 188.8.131.524.
Thanks for the information. I finally managed to get it to work late yesterday afternoon. The instructions were not that clear as it was better to run the script in a command prompt (run as administrator) instead of just right clicking it as administrator.