Small Update i got a lead from reddit :
Does the BIOS have resizeable bar support? I heard that P100/P40 requires this for multiple cards to work well.
i could not locate resizable Bar Support in the American Megatrends Bios ;(
somehow i cannot add pictures here, otherwise i would have share the bios options.
I think you have something here, but probably not leading to a solution. It could be the B250 chipset. I have a Asus B350 with rebar but it's not documented in the
manual so possibly was introduced with B450 and back ported to B350 with a BIOS update. It's unlikely possible on the B250 but if so would require the update from Onda.
The Problem is, Onda is not very supportive at all, as most of these chinese "cheap,cheap,cheap" mining companys...