maybe this: https://picclick.co.uk/Elka-mk-88-Service-Manual-Schematic-Diagrams-schaltplan-schema-144312053111.html
reading the manual for the es9 - I don't think you can use it as a midi to cv module, midi only appears to be used for controlling the internal mixer etc - I think you'd want the fh-2 to do what you want!
"some of the best base-level info to remember can be found in Jim's sigfile" @Lugia
Utility modules are the dull polish that makes the shiny modules actually shine!!!
sound sources < sound modifiers < modulation sources < utilities