I felt inspired to hack on the lx800 and was able to get it to do the self test. It's not perfect, there's still some stray junk, and also some strange vertical blind effects but it's fun to see it do something.
In many ways, it's very similar to the ap2000/lx810l, they're 9 pin printers that do double passes to get NLQ text. It's useful to take some code from the ap2000 and merge it into the lx800.
The lx800 uses a different gate array and things are wired up quite differently. (More gatorade...)
I got the buttons to work, but oddly, if you do a form feed it hangs once it kicks down a page.