this thread is rather old. However the Third Stage Edition is my favorite version of “Dune”.
Since 2014 a German BluRay of the TV version in widescreen is available.
So if Phineas is still reading this he might be interested in doing a HD 1080p version of his Third Stage Edition.
Please respond in the thread or by PM and I could help out sourcing the TV version on Bluray
If the German Blu ray you are referencing here uses the same master as the Japanese Extended Blu ray, then the Extended scenes are just upscaled to 1080p and are not true HD. They are spliced in with the scenes from the theatrical version, which are true 1080p HD. Do you have a link for the German Blu ray?