[sdiy] Polyphonic MIDI to CV???

[KPEEK1 at prodigy.net]

Here is my simplified question:

If I have two monosynth modules and two separate MIDI 
to CV/Gate convertors, then I can play two-note 
polyphony provided the two MIDI to CV are on different 
MIDI channels (eg. Channel 1 and 2)

I order to accomplish this I need to play each note on 
a separate keyboard or input device. I want to make 
something where I can play two and three notes and 
have each assigned to separate monosynth modules like 
the Oberheim SEM 4 voice but using a MIDI controller. 

How can I make it where the notes are prioritized and 
the second note played go to the second monosynth? The 
third note to the third monosynth etc.?

I know some commercial MIDI to CV convertors do this, 
but I would prefer to build one if possible.

Thanks!!!!!!