Sorry, this was ment for the modx forum, but the system doesn't let me correct my mistake... 🙁

When I connect the FC to FC1 it controls the volume of every other instrument, except the one I want, the organ.

And the reason is very important. When we say the word KEYBOARD in a system setup we are referring to not only the black-and-whites, but the MW, the PB Wheel, the Sustain pedal, the Foot Controllers, etc. Keyboard includes all of these.

When your keys aren’t controlling the organ then neither are the MW, PB Wheel, Sustain pedal, Foot Controllers, etc.

As you have discovered, the Super Knob, being “super”, can control any or all of the 16 Parts via the Control Assign matrix. This way you can control the output level of a Part not under KBD CTRL. And because the Super Knob can be linked to either FC1/FC2 as you desire, you can control it with your Foot.

The Super Knob can be linked to any of the 8 Common Assign Knobs. When linked, they move when you move the Super Knob. You can program “how much” and in which “direction”.
Then at the Part level of the architecture, the Part’s VOLUME can be set as the Destination for one of the Part Assign Knobs.
Each of the 16 Parts has its own 8 Part Assign Knobs.
When you directly *select* a Part, the 8 Part Assign Knobs for that Part occupy the 8 rotary encoders. (Assuming [ASSIGN] is lit).
When you select the upper COMMON level the 8 Common Assign Knobs occupy the rotary encoders
You can choose to link any of a Part’s Assign Knobs to a Common Assign Knob, which as we know responds to the Super Knob.

You don’t want to link everything to the Super Knob... from each Part, you decide which parameters you want access to all the time.
By linking the Part Assign Knob with one of the Common Assign Knobs, you have made it possible to control it by moving the Super Knob.
And unlike the Common and Part Assign Knobs, the Super Knob is always accessible — no special screen or button needs to be lit or active.

If you think of these interconnections as the workings of a watch, or a series of gears and pulleys that can be interconnected, you get an idea of how this all works. What it allows is - the ability to precisely change more than one parameter with a single control gesture. Each parameter value can be made to change the amount and in the direction you design... and, as this clearly shows, across multiple Parts (whether or not under direct KBD CTRL)!

And I don't suppose this would work for the sustain pedal. Maybe there's another way?

Sustain pedal and it’s behavior present a different set of issues. As stated previously, the Sustain function is a KEYBOARD function. And goes along wherever the rest of Keyboard Controllers are going. There is no Super Sustain function that we can separately use to control the externally controlled organ (?) instead the Sustain pedal will go to Control the same sounds the keys are triggering.

Your external controller should be used to send Sustain messages, cc64, to the Part or Parts you want externally control. If you are using your external controller, use a sustain pedal connected to it... to ensure the most musical/typical behavior. (That is not to say you couldn’t find a way to implement sustain another way but it might have nothing to do with how you’d like to control it. I’m thinking changing AmpEG parameters — but this will not give the same behavior as getting a proper sustain pedal plugged into the Keys you are *playing*.

Thanks a lot for your quick and very clear response.