let me say that you're doing a great job here!
Thanks. This clone is unique among others -- its video controller is almost, but not quite, entirely unlike CGA: it doesn't use a mc6845, always runs in graphics mode, but you still can set a text mode via standard CGA ports. Any access to those (and video memory in text mode) causes a NMI, and its service routine does the rest.
Fortunately, there is BIOS source (that doesn't quite match the binaries) and technical manual (for a pre-release hardware) and a set of schematics (for two different hardware revisions).