Thanks falotico for bringing this topic back up. It's very interesting about Mannes/Godowsky and drying the film before the diffusion process. That's an interesting point...

I think the strength of the Capstaff process is in the dye colors. I've seen them and I don't think that a mixture of typical CMY dyes would really do the trick. Of course you can make any color (in theory) with CMY, but in dye-imbitition systems the dyes cannot be mixed and expected to give a neutral scale since each dye's contrast curve is related to its own particular pH. So although you could match the color with a mixture of CMY; a mixture probably wouldn't work in the process.

So the trick is to find 2 dyes, with the right "pina" properties and the right colors. An experienced colorist could probably look at examples of the two dyed members of a 2-Color KR and give some suggestions for acid dyes that may work.