HELP !!
Has anyone used the assignable footswitch in performance mode? .. and could deselect it 'off' on selected parts? eg; I only want it to function on part 1. Parts 2,3,4 I don't want it to have any effect. I've followed the manual and I just can't get it to function as described.

I'm starting to think that I am missing something here.
I wish to set a simple layered performance using two voices: Piano (assigned to Part 1) and Strings (Assigned to part 2). In permformance mode, I want to set the Strings voice to only respond to the Assignable Foot Switch (which in Utilities I have assigned it to Midi CC 66 .. sostenuto) and not the sustain pedal. I only want the piano voice to respond to the sustain pedal and not the assignable footswitch. I am thinking this should be straight forward.

This is not straight forward at all. Both cc64 and cc66 are messages treated by MIDI as “Hold” messages (Hold1 and Hold2). If you disable Sustain (SUS) for a Part by turning its RECEIVE SWITCH = Off, both Sustain and Sostenuto behaviors are defeated. They are treated together.

In a similar fashion to Volume and Expression (cc07 and cc11) which are treated by MIDI as “output level” messages. They too, are treated together.

Add to this that selecting a cc (Control Change) number that has a *dedicated function* is problematical when there is a separate option to defeat that control specifically. For example, if you assign FC1 to Expression (the default) you cannot and do not prevent a Part from responding to Expression by setting the FC1 RECEIVE SWITCH = Off. That will not work... there is a specific entry to prevent VOL/EXP. This allows the FC1 to still function doing other things.

So setting the Part to ignore FC1 is not sufficient to block it from responding to the Expression message. If you don’t want the Expression function it would be wise to program another cc number (one without a dedicated function). However, if you were to go into the CTRL SET of a Voice (in VOICE mode) and assign “AEG-Attack” to FC1... when you placed this VOICE in a Performance, defeating/activating FC1 will stop and activate the pedal from adjusting the AEG-Attack, but will not affect the role of the FC 1 as Expression. Expression is a dedicated function.

Conversely you could deactivate the Receive Switch for VOL/EXP without defeating the FC1 entirely.

If you set the Assignable FS to a cc number that does not have a dedicated function, for example, cc90, you could within a VOICE (CTRL Set) assign this to any function you want to jump to On(127) when pressed and return to Off(0) when released. For example, MONO/POLY... the FS would swap polyphonic play with mono lead by FS. Setting the Receive Switch Off simply deactivates this.

If you set the Assignable FS to cc66 (Sostenuto) you activate the special HOLD2 (Sustain) function for this controller, if you program a Voice to do something with FS say, “PCH-Crs” (Pitch-Coarse tune) you will get both sostenuto behavior and Pitch when you engage the FS. The sustain function (sostenuto) can be defeated in a Performance by setting the SUS “RECEIVE SWITCH” = Off. Independently the FS can be activated/deactivated - this will only deactivate the Pitch-Coarse behavior.

You cannot have separate sustain and sostenuto behavior as you are trying to do.

Thank you Mr 'Bad Mister' for clarifying that for me. I really appreciate you spending the time to provide me with a detailed response.
Cheers
Stephen