I didn't play around too much with SynthEdit, but you need 2 outs (I don't mean the soundout!).

In export settings ther's some stereo option that is greyed out normally if you don't have a "pair" of outputs.
Here is the cubase warning for Chellofan:
Cubase Elements Warnings (Tuesday, January 10, 2017)
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This mixer configuration expected "Cellofan" to have Output 1: Stereo,
-> The instrument currently has Output 1: Mono,
-> The instrument channel will be silent.
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