Hello,
The Gecko drives are driven by step and direction signals instead of the normal +/-10vdc other amps require. You will need to configure your Galil for step motor operation to the Geckos. Hooking up the encoder signals to the Galil is not necessary. The Gecko will take the step pulses from the Galil and move the motor\encoder the same number of steps. Direction signals are only pulses internal to the drive at the start of a move sequence to determine which way the motor rotates.
The Galil works fine for driving the Gecko servo drives although if you want better low speed torque, you may want to consider stepper motors and drives or gear reduction of your servo motors.
Hope this helps,
Allen