You're not the first to discover what is the only satisfactory way to use any of the Durst AC enlargers to print B&W but you've certainly documented it better than anyone else! Many folk who have acquired one of these have wasted endless hours trying to find a way to make them work in their native additive mode using blue and green exposures onto multicontrast paper. Sounds good in theory until it is realised that there is no way provided to control the duration of the the exposures.
The automatic exposure adjustment according to head height is one of the great advantages of these enlargers. I can take autofocus on enlargers or leave it - Durst were obsessed with AF but at least the computerised sort can be easily readjusted for different lenses or when focus goes out of whack unlike many older Dursts (and other brands) that used cams.
I mainly used my AC800s (I have 3 of them) for production colour printing but they have not been used for some years. I will keep your site in mind when it comes time to dispose of them. I will most probably sell them for parts. I do have the circuit diagrams and a service manual but the manual is of limited value without a diagnostic tool that Durst suppied but I don't have. It is also written in the same stilted style of English you mention in your post. A piece of trivia that may be of interest: the microprocessor in the AC800 is a Zilog Z80 as was used in many 8 bit PCs in the 1980s. OzJohn