Michael,
The shortest Ethernet can do is 160 meters (and that is from gear from 30 years ago). So it can't be the length.
Btw, you could test the cable by connecting your Mini to it, I suppose ?
I presume that when XXHE is installed the default state is that the W10 Updates is blocked.
That depends. For normal RAM-OS Disk situations (they are sold separately just the same) this is not the case. For dedicated installs like yours it depends on whether I think of it. Point is : the Audio PC is regarded not to be connected to te Internet at any time (it can of course, but there you go with problems - not today then tomorrow).
Because your "install" took quite many hurdles, I did the install many times. So actually I don't know. But apparently I did.
Regards,
Peter