So what version of firmware are you using? (I mean, where did you get it from?) Lanthan's amendment is in more than one place, his code, my code.
The Kritzler code uses
MotorA step - pin 9
MotorA dir - pin 10
MotorB step - pin 11
MotorB dir - pin 12
So I'm guessing your wiring reflects that?
The test code you have has motorA (x) on
dir - pin 8
step - pin 9
enable - pin 10
So that doesn't match the kritzler code - not sure why it works for you.
Probably isn't a driver issue if you're getting movement using the test sketch.
The most recent version of the controller uses new comms protocol, where it appends a CRC rather that does a reply and confirm to make sure it's got the right command. I'm pretty sure all the firmwares I've published have been updated to do this, but I'm also pretty sure none of the firmwares I've published have their stepper pins mapped out the same way as der kritzler, so all of them will require a minor amendment to get them to work. If you haven't done the amendment, then that's probably the problem.
If the commands are disappearing out of the command queue in the controller quickly enough (the status line goes yellow, and says "BUSY ... " for a second), then the communication is working ok.