Sebastian,
Like my colleague, I am struggling with the same issue. When you say "simply unzip" the upgrade package, I have no idea from where you mean. Do I upload it from Host > File manager in my parent portal whiile logged in and then recycle the URL to the portal root? I have no idea where I am supposed to be when I "unzip" it. I have successfully added 3rd party modules to my 4.8.4 parent portal, and a range of other Host tasks.
I am very very pleased with this outstanding content management product, and most things I have found answers for. This question has taken me an hour just to find this forum thread.
I will be most pleased for any answer you may offer to clarify this. Danke Schoen.