Ron, I think your motors where just rated too high a voltage. I think if you had 2V motors, you would have gotten acceptable performance.
I bought the xylotex kit, with their motors, board and power supply. When I found them to slow I replace the board with geckos and raised the power supply voltage to about 48v. That worked well.
The simple fact is that voltage equates to speed with steppers, and the Xylotex board with its 24v useful limit is just slow. With the Gecko 251s available (they were not when I started the project) I see no reason to ever buy a Xylotex board.