For many years I have been building multiple powered diesel units with a single Cruise Commander. With some modifications, it can handle four can motors just fine.
Since the drive transistors have super low turn on resistance, the limiting factor is the current rating of the bridge rectifier. I put a heat sink on the rectifier with heat transfer epoxy and mount a computer fan blowing directly on the heat sink. Works great.
I have at least four loco sets with four motors and one loco set with six motors.
Some months ago, I put a CCM into a K-line A-B-A with six motors. The motors are wired in series/parallel - each unit has the motors wired in series and the units themselves are wired in parallel. A small computer fan nestled between the drive transistor heat sink keeps the rectifier cool enough. The CCM has a different bridge rectifier that does not lend itself to mounting a heat sink as easily as the full Cruise Commander does.
The funny thing about this K-Line six motor A-B-A set is that it had a tether with only four wires. Two wires ran the additional four motors and one ran the rear headlight and one ran the rear coupler. That meant all the power/ground pickup was in the forward A unit. I rewired the tether so that the B unit also provided power and ground and phooey on the rear headlight and electro coupler.
This loco will pull a passenger train, so not a lot of uncoupling will be going on.
