Yep, in Marlin 1.9 I had following:
Code:
#define MIXING_EXTRUDER
#if ENABLED(MIXING_EXTRUDER)
  #define MIXING_STEPPERS 2        // Number of steppers in your mixing extruder
  #define MIXING_VIRTUAL_TOOLS 16  // Use the Virtual Tool method with M163 and M164
  #define DIRECT_MIXING_IN_G1    // Allow ABCDHI mix factors in G1 movement commands
#endif
The virtual extruders are kind of a preset mixing values to use. To use the 16 virtual extruders, in start gcode I defined the virtual tools by assigning the mixing ratios for each. The mixing ratios are what I thought would be good, but they can be anything as long as the total value is 1. So when selecting T5 for example, would drive 21% E0 and 79% E1.
https://marlinfw.org/docs/gcode/M163.html
Code:
; Virtual extruder 0
M163 S0 P1
M163 S1 P0
M164 S0 P1

; Virtual extruder 1
M163 S0 P0
M163 S1 P1
M164 S1 P1

; Virtual extruder 2
M163 S0 P0.5
M163 S1 P0.5
M164 S2 P1

; Virtual extruder 3
M163 S0 P0.07
M163 S1 P0.93
M164 S3 P1

; Virtual extruder 4
M163 S0 P0.14
M163 S1 P0.86
M164 S4 P1

; Virtual extruder 5
M163 S0 P0.21
M163 S1 P0.79
M164 S5 P1

; Virtual extruder 6
M163 S0 P0.28
M163 S1 P0.72
M164 S6 P1

; Virtual extruder 7
M163 S0 P0.35
M163 S1 P0.65
M164 S7 P1

; Virtual extruder 8
M163 S0 P0.42
M163 S1 P0.58
M164 S8 P1

; Virtual extruder 9
M163 S0 P0.49
M163 S1 P0.51
M164 S9 P1

; Virtual extruder 10
M163 S0 P0.57
M163 S1 P0.43
M164 S10 P1

; Virtual extruder 11
M163 S0 P0.64
M163 S1 P0.36
M164 S11 P1

; Virtual extruder 12
M163 S0 P0.71
M163 S1 P0.29
M164 S12 P1

; Virtual extruder 13
M163 S0 P0.78
M163 S1 P0.22
M164 S13 P1

; Virtual extruder 14
M163 S0 P0.85
M163 S1 P0.92
M164 S14 P1

; Virtual extruder 15
M163 S0 P0.92
M163 S1 P0.8
M164 S15 P1
But this method gives only 16 gradients. The proper way to get full mixing steps is to use M165 in the gcode file.
So to get a gradient sweep with 2 colors is to add following codes per layer
M165 A0 B100 ; layer 1
M165 A1 B99 ; layer 2
M165 A2 B98 ; layer 3
etc.
(For 3-color mixing, add C: M165 A1 B99 C0)
https://marlinfw.org/docs/gcode/M165.html

Sadly no MMU2S, no info or anything. Might ask about the status, it's been quite more than 3 weeks already...