Nice screens!!!
The update issues (new Kernal - must get the current bootloader to look at the updated grub.cfg ...) have me using more disks and cmos to switch much more often.
I am working on a project[1] I hope to use to share more Linux later but right now I am not ready to help you with you issue right away and will be spending more time in the various resources (e.g. [2]) to begin to get a handle on the issues you bring up.
Besides obtaining the grub2 manual perhaps a place to start are the /etc/default/grub file and /etc/grub.d folder (script 05 perhaps?).
I will be working on the project next Tuesday. I would love to hear about what you find.