> I boot the linux kernel frem an USB and then linux itself from the HD. [...]
> I think that boot from SIL3114 is not supported on X5000 or is it?

The fact that you don't run the Linux kernel directly from the SiI3114 may indicate that the X5000 U-Boot cannot boot it from the SiI3114, for whatever reason. If that's the case (in contrast to what I wrote in that other thread), the MorphOS boot.img cannot be booted from the SiI3114 either, nor anything else for that matter.

> does it need another hidden partition as it does on a Mac.
> [...] Do I need any hidden partitions or?

In case you mean the 128 MiB padding partitions between your normal partitions, then no, they are only required on the Macs. In case you mean the partition where the MorphOS boot.img resides to be different from the partition where the MorphOS system files reside (as done on the Pegasos I and on the Macs), then this may be necessary if U-Boot cannot access the MorphOS system partition.

> I have searched in Uboot for the MorphOS boot variables so that I can
> tell it where to look but did not find any.

"Before installing MorphOS, please make sure that your X5000 device has been updated to a firmware version that supports installing MorphOS."
https://www.morphos-team.net/installation

Did you do this?