Somebdoy?

Is there a simple way to make the sound in the SONG MODE to sound exactly the same as in the VOICE MODE?

You must make it sound like you want for this particular new environment into which you have placed it. Voice mode is like playing your piano at home, then taking that piano to the recording studio (Song mode). It is a different room (this means it will have different effects) and will undoubtedly sound different because of this.

Think about the real world for a minute... It will better help you understand what is happening and why. In VOICE mode the instrument sound is in a room - all by itself - where it has exclusive use of the Insert Effects, the System Effects, and the Master Effects and EQ. The Insert Effects are apart of the instrument; System Effects are room acoustics and time delay type effects and are external to the instrument sound; Master Effects and EQ are overall and certainly external to the instrument.

When you pack your instrument up and place it in a PART (either a Performance Part or a Song/Pattern Part) it is like packing it up and moving it to the studio... Where you are now plugged into a Mixer shared by as many as 15 other band members (if Song/Pattern mixing is used). This mixer belongs to the studio!

Each instrument has a channel on this Mixer. The studio's mixer starts with all Volumes at 100, all Pan positions set to Center, all Reverb Sends set to 12, all Chorus Sends set to 0, all EQ's zeroed completely out. It starts in a rather neutral state.

If you've ever played in a band, it's like VOICE mode is you alone, MIXING mode is like going to the studio where some of your settings are turned over to the engineer running the mixer. At home your Volume might have been maxed out 127, when you share the mixer with 15 other musicians, your volume is by default reduced to 100, at home your Reverb TYPE and Chorus TYPE was yours to choose - and could be set JUST for you. Now you *share* these effects with the band... Your channel has a SEND (much like an AUX SEND) on your channel of the mixer, same as every one of the other 15 musicians plugged into the mixer. All 16 of you *share* the same room acoustics (Reverb Chamber) but each of you has your own Send amount. This works because the goal is to make the band (the ensemble) sound like they are playing together at the same time in the same place!

And so on, it is these things that sound different. And rightfully so. Because you need to make a "production decision". Now that you are in a room, in theory, with 15 other instruments... You cannot all bring your room acoustics (reverb) from home, you all must share the acoustics of the studio. Make sense? You must now decide how much reverb is right for this ensemble - at home in Voice mode only one sound was playing, now that you're in with the band the amount of Reverb will necessarily need to change , so will the EQ settings, and so on.

In the real world one instrument alone sounds very different when placed in an ensemble. You task is NOT to make it sound like it did in Voice mode, but to make it sound right in its current surroundings. Newbies think there is some advantage to hearing it sound exactly the same. Fundamentally it is the same, what's different is the added features (reverb, chorus, EQ, volume, etc.) when you are in MIXING mode (it's a verb) it's your job to create a MIX = a new balance of the instruments so they work in this new context.

Trust me on this I spend years as a recording engineer. It's all about how you make the instrument sound in its new surroundings. If you think EQ'ing the acoustic piano that is playing in a string quartet environment will be the same as the EQ when you put it in with a rock guitar power trio, you'll learn it is NOT going to be the same. Each requires your listening attention to make it match the New environment in which you are placing it.

So what's different: the Reverb Type is likely different... All 16 Parts cannot bring there System Effects from Voice mode
The Chorus Type is likely different... Same reason
The Volume is likely changed to allow room for additional instruments
The Send amount to the Reverb and the Chorus is highly subjective and changes with the number of instruments playing. You might need more, you might need less.
The EQ is likely different... In the studio the channel is set "flat" because you need to adjust the frequency balance based on what types of instruments you are putting this instrument in with.

It does not sound the same in the new mode, because it shouldn't. Embrace it, it is how the real world works, it is how your synth works.

If you are interested in more information about the extensive processing in your MOXF we recommend the following article;
Introducing the MOXF Effects

I, too, have an effect problem! For some reason, when you change the output to USB 1-2 in song mode, the system effects don't work! As soon as I change the output back to USB 3-4, the system effects work again! I need to use USB 1-2 in order to record to my software on my computer, and I need the system effects to work on these channel as well. How can I get the system effects to work when output is changed to USB 1-2?