Having watched some video demos of vintager Oberheim synths
, I wonder whether that "Oberheim sound" actually requires a decent number of polyphonic voices.
The question is what actually defines the Oberheim sound for you. If you go for the classic SEM sound, the YouTube list you've posted doesn't feature any of that with the exception of the OB-6, which is compared to the OB-Xa in one video although it doesn't make any sense other than comparing the number of blue stripes, since the OB-6 has no historical predecessor. It utilizes the resurrected SEM oscillators and filter in conjunction with the basic architecture of the Prophet-6 that in turn received an expanded modulation section due to the filter specific options. But the OB-Xa utilized curtis filters for example, which actually makes the Prophet '08 closer to it in that regard rather than the OB-6.
In general, none of the polyphonic Oberheims featured the classic SEM multimode filter. Neither the OB-X, nor the OB-Xa, OB-8, or the Matrix 12, although the latter's filter comes closest in terms of flexibility.
On the other hand, combining a couple of SEM modules will not resemble the OB-6 either. Like LoboLives mentioned, you'd end up with a huge sound, basically that of the Four and Eight Voice. That's also why a Two Voice Pro still sounds different from an OB-6, whether you play it monophonically, duophonically, or with voices that are hard-panned to the left and the right, because you get twice the amount of articulation, which eventually makes it sound much bigger.