I've used the Pro-2 to mimic not an OB-6, but a Tom Oberheim SEM, using the Pro-2's SEM filter.
There are some things that need to be adjusted as far as the filter tracking (highly non-linear, even when keyboard tracking is off at the SEM), and the base Pro-2 digital oscillators lack the fundamental that the SEM oscillators do (so one ends up using the remaining two oscs as sine to beef up the sound).
But it can be done–just not paraphonically–and sounds pretty good when each unit (SEM and Pro-2) are panned to 10 and 2 on the clock.
I'd guess that the same applies to the Prophet-6, and perhaps the OB-6, by extension.