IRRC it doesn’t do that, anyway, there are only limits for GRAINS and PMD, but for all other engines you can distribute the voices as you please, as long as every slot has a minimum of one voices.
I think this is closely related to the Midi Engine, because that always has a voice count of 0, so if you select two MIDI engines, all voices should be available to the remaining slot(s) anyway. I don’t get why these are two wishes, the point of the MIDI engine is to save CPU, if that is not made available to the other slots that would defeat the purpose entirely.
I think you are mistaken, Tasty Chips started shipping the GR Mega in July 2024, but there’s a still waiting list because there is more demand than what they can produce.