Originally owners of the Four-Voice could expand it to up to eight SEM modules. Shown here is an example of just that. This became the first Eight-Voice.
Later Oberheim released an Eight-Voice with two keyboards, (one on top of the other: the top one, a 4-octave(C-C), 49-note, and the bottom one, a 5-octave(C-C), 61-note) and an onboard Digital Programmer which held 16 presets. Currently we have no picture of this one.
Dennis DeYoung of Styx - used extensively on Pieces of Eight (1978),
Brian Kehew and Roger Manning of The Moog Cookbook,
Geddy Lee of Rush,
David Palmer of Jethro Tull,
Tim Simenon of Bomb the Bass,
Akiko Yano of Yellow Magic
[Let us know if you have any further additions to this list.]