About grub gfx and isolinux gfx, I have some information, but I am still looking for more knowledge. isolinux will need to be able to use source files from gfxboot-theme package (source package, plus gfxboot installed, and a related devel package). I don't know yet how to change the files in the source package, I hope to find someone who will teach that to me, because I didn't find any documentation.
Here is the Debian package for that:
http://packages.debian.org/en/source/wheezy/gfxboot-themesGrub does not need anything else than a tool to help customize the files : I gave you the name, I think if you first grab the deb file for ubuntu and install it to Debian it has chances to work, then you will just have to copy the grub files of you box to your build directory if you use a chroot method, or leave it as is if you use remastersys.
Else than that, there are docs out there, and I think there is even a chan for grub2.
perhaps the tutorial here could be interesting:
http://www.dedoimedo.com/computers/grub-2.htmlIRC might be #grub on Freenode. I found the info on the web and didn't check.
Which one or the two gfxboot do you want to try first ?