Doepfer

> The 258 seems to be described as a vco, and the 259 as a 
> 'waveshaper'

The 258 is a "Dual Oscillator" and the 259 is a "Programmable Complex 
Waveform Generator" is also dual but have a dedicated modulation VCO to 
the "main" oscillator.
you can compare schematics for the 258 and 259 here:

http://home.swipnet.se/cfmd/synths/companies/buchla/