Hello,

> > This is Open Firmware 1.0.5 and System Disk doesn't work properly,
> > only BootVars.
> 
> You might have the wrong version of System Disk.  You'll want 2.3.1.  It
> has the facilities to set the input and output devices as well as the
> boot device and file.  This was removed from later versions.

None of them work properly with an UMAX S900 as far as I know, although some MacOS versions think it's a PowerMac 8500 for some reason.

have fun
Michael