I found out a while ago that there was a likely-dumpable MCU on the Triforce that is needed for emulation.
The datasheet didn't mention any protection so it was worth trying. The problem was the adapter needed for it isn't cheap but I got around to getting it and Mark F. loaned me several Triforce sets.
I don't know where the "boot rom" in mame came from or why it doesn't even have an extension but, it looks like this thing went through lots of revisions and also has readable chips that aren't in mame yet, no idea why.
The MCU was readable as well as a couple of other chips so far, from this one: