[p750mmx]

Unfotunately MiBox 3 only gots USB 2 ports...I don't think that it will handle a USB3 > Gigabit LAN (1000M) adapter...  

That's not the case. A USB 3 Gigabit adaptor will work in a USB 2 port and deliver ~300Mbs Ethernet speeds. It won't deliver full Gigabit speeds but will massively outperform a 100Mbs USB 2 adaptor, and should be more than enough for UHD BD rips.

That's why we recommend USB 3 Gigabit adaptors for USB 2 devices like MiBox, FireTV Sticks etc., rather than USB 2 100Mbs adaptors.   

And the Mi Box S also can't handle this media, even when the network speed goes up to 300Mbit with a USB adapter. It is just to much for the little box.
This media (that I also tested as UHD100), is quite exceptional. There is a lot of HEVC media that goes well with this box, but that is not one of them

Edit: @Messatsu I should have quoted you...