It sounds like the controls you used previously may have been a
VXM-1-1 where you had motors 1 and 3
If you do not need to move simultaneously you could use a VXM-3
(Basically the same setup with 2 Vxm's bussed together controlled by
1 serial port but now you would have motors 1,2, and 3)
If you need them to move simultaneously then it gets a bit more
difficult and needs more than 1 serial port.
Cliff