Boy, I understand the confusion...
Here's my best stab at it.
The highlander has both the MGR and a motor integrated into the main motor's transmission.
As you can see, the full cabability of these motors is not available at the same time.
My best guess is the pack cannot produce enough current to supply both motors . . .
and/or the controller's voltage booster is the limitation. When a system uses a booster to change the voltage from say, 288VDC to 650VDC, the full power used needs to be "processed" with the two IGBT's in the doubler circuit. Thus, they must be rated for, say 50kW at 288V. This means they must handle the full voltage - 650V AND the full current of the battery pack - 175A in this example. So, from the voltage doubler perspective, you've got the worst of both worlds - high current AND high voltage.
Now, about the MGR, that 50kW is intermittent. Better to plan on 25kW most of the time and 50kW for short bursts, like getting on the highway.
Also, in the stock mode, it is CRITICAL that it is mounted with the motor in front of the axle. Why? because oil is pumped by the ring gear into several oil gallies at the top of the MGR, then distributed to the gears and bearings and cooling for the stator. This won't work in reverse, so a backwards mounted MGR will overheat and wear out quickly.
HTH,
E*clipse