Here is the thing then: the 640 does work now with PC-Link and M-Crew. (See my uncut, lame video at the end - "Welcome to Paradise" :-) .)
Yes, it is done, and I feel this is a breakthrough, after all those unsuccessful tries in the past, including my previous attempts back in 2017 or so. The icing on the cake is the 640 has kept all its keyboard functionalities too !
I guess what you are mostly interested in is how this was made possible, and what's needed to replicate it on your machines - the shiny, polished, step-by-step guide and documentation I originally wanted to post here can w