If I had to guess, Roger used the famous 4-0perator yamaha patch "Sync Lead," perhaps tailored a bit with his own portamento settings and such.

DX=100's are going for "crazy stupid money" these days, so might I suggest the Tx81z.

The voice archetechture is a lot cleaner, anyway, and then you can have "lately bass," another staple sound in the history of music.