I really don't know if the older McIntosh processors were based on Marantz processors. I would highly doubt this. As far as the newer processors (MX122 or 8802 or 8801), they are completely different architectures. For one, the Marantz does have individual boards that have discrete audio stages for each output channel. It also has completely different power supply layouts. McIntosh likes to use R-Core transformers and has different stages of power supply voltage regulation. As far as I can tell, all McIntosh processors use op amp for analog stages.
If you hunt for pictures, you'll see that the internals are completely different between McIntosh and Marantz units. It could be that the original firmware of McIntosh was based on a Marantz code. I have no idea on this.