Onyx had a few slots reserved for graphics, original could have more compute boards. But you could certainly put two couple cpu boards in an onyx deskside or rack.
The funny thing was that our Cray sales team, from the C90 and T3D, jumped ship from Cray to SGI before their merger.
So got to set up some Indys as web servers/ Oracle database. Surprise! Same sales team. Then the merger happened and we got the Origin boxes.
Perhaps all the purple rack onyx had been dumped but we dug through ILMs boneyard looking to add to our cxfs cluster, but the FC bus speed was too low.
It is possible that R10k was different or that there were multiple chassis. The desk sides I had experience with required RAM in slot 1, with CPU in slot 2, with up to 4 CPUs on the board.
o200 was more restrictive, with 2 CPUs per chassis, with the ability to cray-link two chassis for a total of 4 CPUs, more required o2000.
But this was a quarter of a century ago or more by now…so I may misremember things.