Dual-boot x64 Volumio and LibreElec?

How do I go about dual-booting x86/x64 Volumio and LibreElec? Better yet, how do I install Kodi in the x86/x64 Volumio OS? I’ve tried but there are so many dependencies missing I gave up after wasting a whole day.

I am also interested in this…

Very difficult, because our setup has been developed as a single OS only, similar to the ARM platforms we support.
With a little knowledge of syslinux configuration (used for legacy bios boot), one should able to adapt the syslinux.cfg file manually without too much trouble. A UEFI boot however becomes a lot more difficult, as the used grub configuration is far more complicated to adapt manually. In both cases, the other OS should be on a different disk.
My advice: don’t try unless you really know what you are doing, we have no tutorials.
And another killer: this will never be supported with a system update, everything will be lost.