Very interesting post. I've seen that approach before being used in Sergei Strelec's DOS section of his distros, for booting different ISOs, IMGs, etc, from a bootmgr menu, but didn't know how those .MBR files (which seem to contain grldr + corresponding boot commands) where generated.
According to your blog post, .MBR files act as the the grldr written to the MBR in our E2B drives, but also includes info about the correct ANGx file to load. And the ANGx files would be the equivalent of grldr at E2B root, but including custom boot command for each payload.
On SS distros, only .MBR + payload pairs are used, there aren't multiple ANGx equivalents at distro root or elsewhere. So my question is: are the .MBR files (as created by EasyBCD) actually required as the entry point in BCD? Could the BCD entry simply point to the ANGx file of choice?
Subject Boot XP VHD from bootmgr blog post.