Both the memory controllers and RAM on the Mx are on die components. The number of controllers (binned) count here. I should have been more specific in what I was saying.

"The 14-core M3 Max only enables 24 out of the 32 controllers, therefore it has 300 GB/sec vs. the 400 GB/sec for all models of the M1 and M2 Max, while the 16-core M3 Max has the same 400 GB/sec as the prior M1 and M2 Max models."