From the following page, an upgrade kit is offered, mainly containing a filament extruder motor with a gear reduction. The gear reduction would give the extruder more force to push the filament in.

The following information I was able to find:

• Increase the E-step value to 400¹⁾.

Extruder Frame Specifications:

• Material: Injection molding plastic
• Driving Gear Diameter: 12mm
• Driven Gear Diameter: 8mm
• Transmission Ratio: 3:1
• Stepper Motor Specifications:
• Motor Type: Bipolar Stepper
• Number of Phase: 2
• Step Angle: 1.8 deg.
• Rate Voltage: DC 3.0V
• Holding Torque:DC 1.2A
• Phase Resistance: 2.5ohms ±10%（20℃）
• Phase Inductance: 3.8mH ±20% (1KHz)
• Rotor Inertia: 30.8g.cm²
• Size: ±63*85*69mm
• Weight: ±290g

After following the extruder intake calibration procedure it was observed that instead of 100mm the intake was only 25mm, So this resulted into the following DEFAULT_AXIS_STEPS_PER_UNIT in Configuration.h:

//Old value: #define DEFAULT_AXIS_STEPS_PER_UNIT   { 160, 160, 800, 185.20 }
#define DEFAULT_AXIS_STEPS_PER_UNIT   { 160, 160, 800, E779.80 }

And after performing a second calibration, a distance from 19.9mm was measured, resulting in the following:

//Old value: #define DEFAULT_AXIS_STEPS_PER_UNIT   { 160, 160, 800, 185.20 }
#define DEFAULT_AXIS_STEPS_PER_UNIT   { 160, 160, 800, E780.58 }

If other problems appear with filament not being able to pushed in, also the Zeelo dual drive extruder/motor could be a solution.