Looking at the specs it would seem that the 20a board would be sufficient, can you set the Rutex drives to limit the 13 amp stall current of those particular motors? If you have the motors then I would think Rutex would be the one's to ask, also you should ask them what the minimum motor inductance can be used with their drives, the motors show 2.5mHy. If the motor inductance is lower than the amp recommended then series choke should be added.
Al.
CNC, Mechatronics Integration and Custom Machine Design
“Logic will get you from A to B. Imagination will take you everywhere.”
Albert E.