Tell the sound crew the MOXF Output is "unbalanced" and they should be using a TS cable (Tip-Sleeve).

It sounds like they maybe using a balanced TRS cable (Tip-Ring-Sleeve) which would be incorrect.

Thank you so much for the quick reply. I passed it along to the guys on the sound system and they are still trying to get it all figured out.
I offered to bring the MOXF to the church to try solutions and offered to buy any necessary special cables.
On another note, I read something recently about some voices on synths sounding flat rather than full if hooked into L/Mono rather than stereo?
Is this another issue with getting best sound out of the MOXF in the church setting? If so, what's the fix?

When listening to music, in general, stereo sounds better than mono. It gives the listener a sense of "space". Stereo requires two speakers with some distance between them. This placement allows for the illusion that items within the field can move, or can seem to be located at specific points in between. It is this illusion that is fun for the ear-brain to interpret sound. It gives it a dimension.

Not all sound systems are setup to reproduce stereo. After all, it does require twice the work and specific gear to make it work. Not only do you need two speakers, you have to have a mixer and an amp that also support stereo. It is more work, for sure.

We've been listening to music in stereo since the late '50, early 1960's... it has become a part of the synth because of its expanded role in doing emulations of other instrumen. A String Orchestra program, sampled and played from the MOXF in true stereo, does indeed, sound bigger, fuller, richer, and more satisfying. No doubt. To the audience instead of your instrument being located in the middle of the stage, it seems to span the stage without having to be louder.

The original pipe organ actually surrounded its audience with sound. The church building itself was designed to reflect the sound of the organ down on the parishioner... the high ceiling to accommodate the 64 foot pipes...

To be fair, it is not always necessary to have your synth in stereo. It's good when the synth is asked to play multi-timbrally, like when playing with drums and arpeggio parts, etc., this is when stereo is Essential. But that is not always the case. After all, you may not always be playing that type of role in your situation.

But stereo, is usually worth the trouble when the best sound is what you're after.

Play your MOXF in headphones. The personal nature of the sound environment will speak for itself.
Play your MOXF in the sound system in the church (or have someone else play while you listen), is the sound what you've come to expect. If not, one of the things missing might very well be stereo!

When playing the MOXF in a mono setup, try the mono version of the "Full Concert Grand"
I believe it's called "Monaural Grand"
See if it doesn't come across sounding more towards what feels right.