Migration assistant is intended - especially in that era - to be used during the initial setup. The best option is to make a full clone of your real system (carbon copy cloner) to a USB drive, and plug that USB drive into your new host, then during the initial OS install (before you create a user), plug the drive in and attach to the guest. Then migrate from other computer will work.
Ethernet, USB to USB and thunderbolt will not work with a guest.
