A/UX will run perfectly happily off a “virtual” scsi2sd disc. That is how my installation is set up: multiple virtual devices for a recovery disc, two MacOS versions and A/UX. Never tried it on a IIfx, mind, but it ought to work.
Mostly a combination of the Macintosh Classic schematic (a cost reduced SE that also uses the same BBU), and backtracing pins on the board. Sprint has this wonderful 'test' feature - click on any pin of the BBU, and you can see exactly where it goes. I'll send you the sprint layout file if you like, you can take a look yourself.
I have one of these massive blueberry monitors and will shortly be able to plug it in to a USB-equipped System 9.2.2 machine, so I'm looking for the software. Macintosh Garden doesn't seem to have it. If you are not familiar there is just a brightness adjust on the monitor itself, every other adjustment is made using software that came with the display.
Actually I think this is it: https://www.macintoshrepository.org/79-apple-displays-software - correct me if I am wrong about that?
That bugs me as well. It also makes less sense because both the vi and vx have integrated video... They should've just created a new schema anyway. "II," as in expandable "Macintosh" (not a compact compact) had run its course really. There were plenty of Mac models that weren't compacts by then. "c" compact II series, moot due to the II series not really meaning anything, so replace it with v? For video???. "x" meaning 030 equipped was also out the door, really. They didn't call the 020 LC successor the LCx.
Tying into the II series was so the slim margin could be touted as being better than the Performa? Whatever, call it the Quadra Jr or something... Or Centris X... Or just suck it up and stick it with the rest of the Performa line... 600, 620, 625...
Boggles the mind.