Okay, here are some basics…

There are two MFX for the four Keyboard Parts (and three more for the Song/Style section). Each one is an independent FX processor. You do not ‘send’ from all of the Parts to it (unlike the main effects Reverb and Chorus processors), but choose which of the Keyboard Parts are routed THROUGH it in their entirety.

Having two MFX means that, for instance, your Electric Piano can get sent to one MFX doing a Flanger, and your clavinet could get sent to a wah-wah AT THE SAME TIME. One overall MFX would mean an either/or, not both.

Think of them as effect pedals like a guitarist uses. They mostly each do just one thing (although their are a few algorithms that have dual effects, like CHO>DIST etc.).

If you look in the Performance edit for each Keyboard Part, you will see a field that allows you to select which MFX (or none) it goes through. This is where you decide (per Performance) how your two MFX are allocated. The default is for UPR 1 & 2 to be routed to MFX1 & MFX2 respectively. But you can change this. Be also aware that in default, the UPR1/2 MFX Link is set to On, so when you select a Tone for either Upper Part, it loads a default MFX for that sound. You might have heard this, some electric pianos come with a default MFX phaser, for instance, or some clarinets load up a wah-wah…

Be aware that, if this Link is on, even if you have set say MFX1 to affect the LWR Part, and set it up carefully, and spent an hour tweaking all the settings, if you then go and select a new UPR1 Tone, it will change the effect and lose all your settings! 🤬. So either temporarily turn off the Link, or make sure you have your UPR Parts already selected before you spend much time tweaking the MFX assigned to the Lower..!