another xen-kernel UEFI story

could someone pleas check this link: 
https://forums.freebsd.org/threads/xen-kernel-doesnt-start-at-all.81556/

does anyone has another idea then duplicating CURRENT and RELEASE via 
Virtualbox or qemu?

XEN simply doesn't boot after setting xen_kernel on in /boot/loader.conf, we 
tried different ways but none worked. It's loading [text], [data], [syms] and 
the preconfig but afterwards there's just the reset-button option, because XEN 
doesn't boot. 

any help appreciated!

lizbeth