I've been having a look at the ComMotion motor driver as an option to drive two motors much like a Sabertooth. With the onboard encoder counting, it should be possible to create something via serial or i2c that acts like a Kangaroo.
My thought is that I could later get two more motors and some omni/mecanum wheels in the future for another platform - or go right for the mecanums now.
Has anyone else made use of the ComMotion? I'd be interested in your feedback (and potentially code!)