Bios doesn't detect all GPUs...

[playfast]

Oh yeah after DDU, disconnect your internet before installing your Adrenalin drivers and reboot, then you can reconnect your internet, that prevents windows from installing generic driver
And last resort you try can the HackFlags 600 registry mod.

[dragonmike]

Nah.
It won't even work with three GPUs plugged in the x16 slots. Also it keeps disconnecting the keyboard plugged in USB. Earlier I had to clear CMOS three times in a row for it to even boot.

I've just ordered a Gigabyte GA-H110-D3A for £45 - will arrive tomorrow. I'll then just transfer over the Celery and the ram and re-plug all cards in it.

[playfast]

Oh sorry that sucks, too late for that mobo I guess the only other fix I could think of was to try PCIE expander boards.

[dragonmike]

Right. So I swapped out that mobo for a Gigabyte GA-H110-D3A and added a PSU.
Plugged in the first Vega (using riser).
Installed Windows but the display was low-rez and the display adapter soon showed an error 43. Big facepalm moment. Went to sleep wondering how many bad risers could there even be in one batch.

Next day I swapped the riser, rebooted, ran devconsole to re-initialise the card... Bam, works. Installed 18.6.1 drivers.
Plugged the next 5 cards one by one (enabling 4G encodes after the 4th)... and all is good again.

So yeah. The Vegas do not draw less power than before on the Onda board, but at least they seem to work, and I have more overhead in case I need it.