Can you use the 4 knobs to act as volume controls for 4 voices in performance mode

Yes, you can. Simply press both [KNOB CONTROL] buttons simultaneously (all six lights illuminate to indicate side-by-side operation.

The top row of (4) knobs become PART VOLUMEs for PARTS 1-4, while the second row become (4) PAN controls. This is also true in SONG/PATTERN mode where they become corresponding controls for PARTs 1-4, 5-8, 9-12 or 13-16 depending on which Track is selected.

Thanks for your reply. That worked. I have a followup question:

When I press both [KNOB CONTROL] buttons, it displayed all 4 Part Volumes, which is perfect. But as soon as I adjust a knob (e.g. for Part 1 Volume), then it only displays the volume/pan for Part 1, and I can no longer see the volume for Parts 2-4.

Is there a way to keep showing the volume values for all 4 Parts even while changing the volume? The reason I need this is because now the knobs are continuous/relative knobs, so I cannot tell the values just by looking at them.

Is there a way to keep showing the volume values for all 4 Parts even while changing the volume? The reason I need this is because now the knobs are continuous/relative knobs, so I cannot tell the values just by looking at them.

Visual reassurance is understandable - here's what to do

Press [UTILITY]
Press [F1] GENERAL
Press [F6] OTHER
Use the RIGHT CURSOR to "Page" right
Find the KNOB parameters in the left column.
Set the DISP TIME (Display Time) = Off

Now when you adjust either Volume (top row) or Pan (bottom row) the screen will remain showing you your relative Volumes or Pan positions for four Parts. This works for both PERFORMANCES and MIXING setups.
Press [STORE] to make this part of your instrument's System settings.

ALTERNATIVE METHOD: (without turning Display Time Off)
From [MIXING]
Press [F1] VOL/PAN
Make this your "go to" screen while performing (once you've recalled the SONG/PATTERN program go to this screen as it gives you the relative volumes and pan positions of your Parts).
Now when you change a Volume (top row) or Pan, it will revert back to the mixer where you can view your relative Volumes and/or Pan positions.

Hope that helps.

and by the way, you can store this in a performance. when you store it will call up the lights and keep those buttons set to control the 4 parts.

and you can also [STORE] your preference for the Display Time Off by pressing [STORE] while in [UTILITY] mode.