About not seeing the GNU Mach console because the BIOS is started in graphical mode...
if I understood the problem. Reading Grub doc... [This paragraph probably don't work because it says it inform Linux to use text mode] Maybe before grub-mkconfig: GRUB_GFXPAYLOAD_LINUX or using e to edit boot configuration and add: https://www.gnu.org/software/grub/manual/grub/grub.html#gfxpayload they say it set the video mode in which Linux is started... but maybe it would apply to Mach too. GRUB_TERMINAL_OUTPUT=vga_text before grub-mkconfig... I realize that if you are using a CD image... you don't easily control the grub-mkconfig part.
