@3DGarage For reference, here's a config.g (for Duet 2, RRF 3.4.5) published by Modix on GitHub. I'm not sure if it matches your printer, and it doesn't match your 6HC for sure.

; Modix Big-60 V2 to V3 upgrade, Electronics only system upgrade, Dual Printhead ; Configuration file for Duet WiFi (firmware version 3.4.5) ; Generated by Modix - Version 3.4.5 Config B global config_version = "Version 3.4.5 Config B" global generation = 2 ; Version 2 to version 3 printer global printhead = 0 ; Aero printhead global expansion = 0 ; no expansion board is installed global printheads = 2 ; Dual printhead, change this value to 1 to switch it to a single-printhead setup ; General preferences_________________________________________________________ G90 ; send absolute coordinates... M83 ; ...but relative extruder moves M555 P2 ; Set output to look like Marlin M575 P1 B57600 S1 ; Set auxiliary serial port baud rate and require checksum (for PanelDue) ; Network_____________________________________________________________________ M550 P"Big 60 V2 to V3" ; set printer name ;M551 P"MODIX3D" ; Set password (optional) M98 P"config_networking.g" ; load networking settings G4 P300 ; wait 300ms ;M552 P0.0.0.0 ; Uncomment this command for using Duet Ethernet board ; Drives_________________________________________________________________________ M569 P0 S1 ; Physical drive 0. X-Axis M569 P1 S0 ; Physical drive 1. Y-Axis M569 P2 S0 ; Physical drive 2. Z-Axis M569 P3 S0 ; Physical drive 3. Primary Extruder M569 P4 S0 ; Physical drive 4. Secondary Extruder ;Motor to stepper motor driver mapping_________________________________________________________ M584 X0 Y1 Z2 E3:4 P3 ; Driver mapping ;Settings_________________________________________________________ M350 X16 Y16 Z16 E16:16 I1 ; Configure microstepping with interpolation M92 X100 Y100 Z2000 E418.5:418.5 ; Set steps per mm M566 X360 Y360 Z30 E3600:3600 P1 ; Set maximum instantaneous speed changes (mm/min) M203 X9000 Y9000 Z200 E5000:5000 ; Set maximum speeds (mm/min) M201 X1000 Y1000 Z200 E5000:5000 ; Set accelerations (mm/s^2) M204 P500 ; Set print and travel accelerations (mm/s^2) M906 X1800 Y1800 E1000:1000 Z2300 I50 ; Set motor currents (mA) and motor idle factor in per cent M84 S100 ; Set idle timeout - 100 seconds ; Axis Limits M208 X0 Y0 Z-3 S1 ; set axis minima M208 X600 Y600 Z600 S0 ; set axis maxima ; Endstops M574 X1 S1 P"xstop" ; configure switch-type (e.g. microswitch) endstop for low end on X via pin xstop M574 Y2 S1 P"ystop" ; configure switch-type (e.g. microswitch) endstop for low end on Y via pin ystop ; Z-Probe M558 P9 C"zprobe.in" H5 F120 T6000 A1 R0.7 ; BLTouch probing settings M950 S0 C"exp.heater3" ; set probe pin M376 H50 ; Height (mm) over which to taper off the bed compensation G31 P500 X-14 Y21 ; BLTouch X and Y offset from nozzle M557 X{move.axes[0].min + sensors.probes[0].offsets[0] + 1, move.axes[0].max + sensors.probes[0].offsets[0] - 1} Y{move.axes[1].min + sensors.probes[0].offsets[1] + 1, move.axes[1].max + sensors.probes[0].offsets[1] - 1} P10:10 ; define mesh grid M98 P"config_probe.g" ; Load the Z-offset from the config_probe.g file ; The Z_offset value is now set in config_probe.g, not in config.g ; Adjust the values there, do not adjust anything here. ; Heaters___________________________________________________________ M140 H-1 ; disable heated bed (overrides default heater mapping) ;E0_________________________________________________________________ M308 S0 P"e0temp" Y"thermistor" T100000 B4725 C7.06e-8 ; configure sensor 0 as thermistor on pin e0temp ;M308 S0 P"spi.cs1" Y"rtd-max31865" ; Configure sensor 0 as PT100 via the daughterboard ;M308 S0 P"e0temp" Y"pt1000" ; Configure sensor 0 as PT1000 on pin e0temp M950 H0 C"e0heat" T0 ; create nozzle heater output on e0heat and map it to sensor 0 M98 P"PID_tune_E0.g" R1 ; PID calibration ; M307 is not used in this config. The M307 files are stored and executed from the PID_tune_E0.g file. You can verify the values there. M143 H0 S285 ; set temperature limit for heater 0 to 285C if {global.printheads} = 2 ;E1_________________________________________________________________ M308 S1 P"e1temp" Y"thermistor" T100000 B4725 C7.06e-8 ; configure sensor 1 as thermistor on pin e1temp ;M308 S1 P"spi.cs2" Y"rtd-max31865" ; Configure sensor 1 as PT100 via the daughterboard ;M308 S1 P"e1temp" Y"pt1000" ; Configure sensor 1 as PT1000 on pin e1temp M950 H1 C"e1heat" T1 ; create nozzle heater output on e1heat and map it to sensor 1 M98 P"PID_tune_E1.g" R1 ; PID calibration ; M307 is not used in this config. The M307 files are stored and executed from the PID_tune_E1.g file. You can verify the values there. M143 H1 S285 ; set temperature limit for heater 1 to 285C ; Fans & LED_________________________________________________________ M950 F0 C"fan0" Q500 ; create fan 0 on pin fan0 and set its frequency M106 P0 S0 H-1 C"Primary blower fan" ; set fan 0 value. M950 F2 C"fan2" Q500 ; create LED on pin fan2 and set its frequency M106 P2 S0 H-1 C"LED" ; Disable fan channel for LED if {global.printheads} = 2 M950 F1 C"fan1" Q500 ; create fan 1 on pin fan1 and set its frequency M106 P1 S0 H-1 C"Secondary blower fan" ; set fan 1 value. ; Tools______________________________________________________________ ;T0_________________________________________________________________ M563 P0 S"E0 Primary" D0 H0 F0 ; define tool 0 G10 P0 X0 Y0 Z0 ; set tool 0 axis offsets G10 P0 R0 S210 ; set initial tool 0 active and standby temperatures to 0C if {global.printheads} = 2 ;T1_________________________________________________________________ M563 P1 S"E1 Secondary" D1 H1 F1 ; define tool 1 G10 P1 X0 Y51.5 Z0 ; set tool 1 axis offsets G10 P1 R0 S210 ; set initial tool 1 active and standby temperatures to 0C ; Automatic power saving____________________________________________ M911 S22.5 R29.0 P"M913 X0 Y0 G91 M83 G1 Z3 E-5 F1000" ; Set voltage thresholds and actions to run on power loss. Power Failure Pause ; Filament sensor settings__________________________________________________ M591 D0 P1 C"e0stop" S1 ; Regular filament sensor for E0 M591 D1 P1 C"e1stop" S1 ; Regular filament sensor for E1 ; Add-on settings__________________________________________________ ; Primary hotend Clog detector__________________________________________________ ;M591 D0 P7 C"e0stop" S1 L3.2 E10 R10:300 ; Clog Detector E0 [Add-On] ;Secondary hotend Clog detector__________________________________________________ ;M591 D1 P7 C"e1stop" S1 L3.2 E10 R10:300 ; Clog Detector E1 [Add-On] ; Crash detector__________________________________________________ ;M950 J2 C"zstop" ; create Input Pin 2 on Z-endstop to for M581 Command. ;M581 P2 T0 S0 R0 ; Crash Detector [Add-On] ; Emergency stop button__________________________________________________ ;M950 J3 C"exp.e6stop" ; create Input Pin 2 on pin E6 to for M581 Command. ;M581 P3 T0 S1 R0 ; Emergency stop [Add-On] ;M581 P3 T1 S1 R1 ; Emergency stop, pause the print [Add-On] ;M581 P3 T1 S1 R0 ; Emergency stop, pause always [Add-On]

A noticeable difference to your config is in the definition of the X endstop: according to Modix, it is positioned at the low end. In a first step, you need to verify this to match the printer's geometry.

Apart from being quite elaborated, you may want to incorporate at least some of the values Modix has set for Accel, steps/mm, speed changes, axis limits etc. in your own config.g.

EDIT: I was wrong with my assumption of the Modix being a CoreXY - please remove

M669 K1

from your config.