This is something I have always wanted to do.  I don't know if I can pull this off (contraints are time, and energy).  There would be two main components.  A controller card, that would interface between a Midi Interface and the voice cards.  This would be a huge projects.

    Anyway, here is a sketch of a block diagram for the voice card.  I consider this to be the hard part of the project.  It will be a voltage controlled card, although, the voltages will be supplied by an on card DAC and a bunch of sample/hold circuits.  Of course, there will be a tuning problem with the VCO's.  Especially if they are exponential VCO's.

    If you have any suggestions for features, speak up.  It will be a while before any of this gets started (if ever).
 
 

    All for now.