
and more,(for Grand Illusion) Dennis had aquired a new synth called an Oberheim SEM 4 Voice, and began using it on every song, along with the Hammond B3, Arp String Ensemble, Arp Oddesy, a Fender Rhodes, and Yamaha C3 grand piano. The HUGE synthesizers you here on this record are all Oberheim 4 Voice.
Pieces of Eight was released in 1978, on this record, Dennis used the same synths, except he upgraded to an Oberheim 8 Voice, and bought a couple of Oberheim OBX's.
found here :The keyboard across from James Young is an Oberheim OB-1, and was only used to play the song "I'm OK" from the, at the time, unreleased Pieces of Eight album. As you know, "I'm OK" has the pipe organ in the studio recording (which was recorded at the Cathedral of St. James in Chicago). To re-create it live. Dennis DeYoung found that by mixing several different synthesizers, he could achieve a very similar sound live without having to haul around a pipe organ. The three instruments used togther were the Moog Taurus I bass pedals played by Chuck, the Oberheim OB-1 for the midrange section played by James Young, and the Arp String Ensemble for the high end played by Dennis DeYoung.
http://www.cathedralstone.net/Pages/Styx.htm
(I left out some irrelevant bits)
The author also states that in earlier days an ARP 2600 was being used.
Check out that site, has got some cool '70s tour photos, too, showing the mentioned equipment among others, plus some tasty '70s clothing !
Have fun, susiwong