MOTM

You need:

a) a polyphonic MIDI-CV converter. The MOTM-650 has 4 'voices' and can be 
daisy-chained with another one for a total of 8.

b) you need multiple 'sets of voice modules'. The most simple/cheapest would be:

1 MOTM-310 VCO
1 MOTM-490 VCF
1 MOTM-800 EG (same envelope for VCF and VCA)
1/2 of a MOTM-190 VCA

You can 'cheat' 1 step above and use a MOTM-440 VCF (because it has the best 
exponential converter) in self-resonance mode in place of the VCO/VCF, but all 
you get are sine wave out :)

Paul S.